diff --git a/src/main/kotlin/dev/usbharu/hideout/domain/model/hideout/entity/User.kt b/src/main/kotlin/dev/usbharu/hideout/domain/model/hideout/entity/User.kt
index d79d617b..38eb81a2 100644
--- a/src/main/kotlin/dev/usbharu/hideout/domain/model/hideout/entity/User.kt
+++ b/src/main/kotlin/dev/usbharu/hideout/domain/model/hideout/entity/User.kt
@@ -1,7 +1,10 @@
 package dev.usbharu.hideout.domain.model.hideout.entity
 
+import dev.usbharu.hideout.config.ApplicationConfig
+import dev.usbharu.hideout.config.CharacterLimit
 import dev.usbharu.hideout.config.Config
 import org.slf4j.LoggerFactory
+import org.springframework.stereotype.Component
 import java.time.Instant
 
 data class User private constructor(
@@ -145,4 +148,121 @@ data class User private constructor(
             )
         }
     }
+
+    @Component
+    class UserBuilder(private val characterLimit: CharacterLimit, private val applicationConfig: ApplicationConfig) {
+        private val logger = LoggerFactory.getLogger(UserBuilder::class.java)
+
+        @Suppress("LongParameterList", "FunctionMinLength", "LongMethod")
+        fun of(
+            id: Long,
+            name: String,
+            domain: String,
+            screenName: String,
+            description: String,
+            password: String? = null,
+            inbox: String,
+            outbox: String,
+            url: String,
+            publicKey: String,
+            privateKey: String? = null,
+            createdAt: Instant,
+            keyId: String,
+            following: String? = null,
+            followers: String? = null
+        ): User {
+            // idは0未満ではいけない
+            require(id >= 0) { "id must be greater than or equal to 0." }
+
+            // nameは空文字以外を含める必要がある
+            require(name.isNotBlank()) { "name must contain non-blank characters." }
+
+            // nameは指定された長さ以下である必要がある
+            val limitedName = if (name.length >= characterLimit.account.id) {
+                logger.warn("name must not exceed ${characterLimit.account.id} characters.")
+                name.substring(0, characterLimit.account.id)
+            } else {
+                name
+            }
+
+            // domainは空文字以外を含める必要がある
+            require(domain.isNotBlank()) { "domain must contain non-blank characters." }
+
+            // domainは指定された長さ以下である必要がある
+            require(domain.length <= characterLimit.general.domain) {
+                "domain must not exceed ${characterLimit.general.domain} characters."
+            }
+
+            // screenNameは空文字以外を含める必要がある
+            require(screenName.isNotBlank()) { "screenName must contain non-blank characters." }
+
+            // screenNameは指定された長さ以下である必要がある
+            val limitedScreenName = if (screenName.length >= characterLimit.account.name) {
+                logger.warn("screenName must not exceed ${characterLimit.account.name} characters.")
+                screenName.substring(0, characterLimit.account.name)
+            } else {
+                screenName
+            }
+
+            // descriptionは指定された長さ以下である必要がある
+            val limitedDescription = if (description.length >= characterLimit.account.description) {
+                logger.warn("description must not exceed ${characterLimit.account.description} characters.")
+                description.substring(0, characterLimit.account.description)
+            } else {
+                description
+            }
+
+            // ローカルユーザーはpasswordとprivateKeyをnullにしてはいけない
+            if (domain == applicationConfig.url.host) {
+                requireNotNull(password) { "password and privateKey must not be null for local users." }
+                requireNotNull(privateKey) { "password and privateKey must not be null for local users." }
+            }
+
+            // urlは空文字以外を含める必要がある
+            require(url.isNotBlank()) { "url must contain non-blank characters." }
+
+            // urlは指定された長さ以下である必要がある
+            require(url.length <= characterLimit.general.url) {
+                "url must not exceed ${characterLimit.general.url} characters."
+            }
+
+            // inboxは空文字以外を含める必要がある
+            require(inbox.isNotBlank()) { "inbox must contain non-blank characters." }
+
+            // inboxは指定された長さ以下である必要がある
+            require(inbox.length <= characterLimit.general.url) {
+                "inbox must not exceed ${characterLimit.general.url} characters."
+            }
+
+            // outboxは空文字以外を含める必要がある
+            require(outbox.isNotBlank()) { "outbox must contain non-blank characters." }
+
+            // outboxは指定された長さ以下である必要がある
+            require(outbox.length <= characterLimit.general.url) {
+                "outbox must not exceed ${characterLimit.general.url} characters."
+            }
+
+            require(keyId.isNotBlank()) {
+                "keyId must contain non-blank characters."
+            }
+
+            return User(
+                id = id,
+                name = limitedName,
+                domain = domain,
+                screenName = limitedScreenName,
+                description = limitedDescription,
+                password = password,
+                inbox = inbox,
+                outbox = outbox,
+                url = url,
+                publicKey = publicKey,
+                privateKey = privateKey,
+                createdAt = createdAt,
+                keyId = keyId,
+                followers = followers,
+                following = following
+            )
+        }
+    }
 }
diff --git a/src/main/kotlin/dev/usbharu/hideout/query/FollowerQueryServiceImpl.kt b/src/main/kotlin/dev/usbharu/hideout/query/FollowerQueryServiceImpl.kt
index 10be4068..75d27e7b 100644
--- a/src/main/kotlin/dev/usbharu/hideout/query/FollowerQueryServiceImpl.kt
+++ b/src/main/kotlin/dev/usbharu/hideout/query/FollowerQueryServiceImpl.kt
@@ -9,7 +9,7 @@ import org.springframework.stereotype.Repository
 import java.time.Instant
 
 @Repository
-class FollowerQueryServiceImpl : FollowerQueryService {
+class FollowerQueryServiceImpl(private val userBuilder: User.UserBuilder) : FollowerQueryService {
     override suspend fun findFollowersById(id: Long): List<User> {
         val followers = Users.alias("FOLLOWERS")
         return Users.innerJoin(
@@ -41,7 +41,7 @@ class FollowerQueryServiceImpl : FollowerQueryService {
             )
             .select { Users.id eq id }
             .map {
-                User.of(
+                userBuilder.of(
                     id = it[followers[Users.id]],
                     name = it[followers[Users.name]],
                     domain = it[followers[Users.domain]],
@@ -92,7 +92,7 @@ class FollowerQueryServiceImpl : FollowerQueryService {
             )
             .select { Users.name eq name and (Users.domain eq domain) }
             .map {
-                User.of(
+                userBuilder.of(
                     id = it[followers[Users.id]],
                     name = it[followers[Users.name]],
                     domain = it[followers[Users.domain]],
@@ -143,7 +143,7 @@ class FollowerQueryServiceImpl : FollowerQueryService {
             )
             .select { followers[Users.id] eq id }
             .map {
-                User.of(
+                userBuilder.of(
                     id = it[followers[Users.id]],
                     name = it[followers[Users.name]],
                     domain = it[followers[Users.domain]],
@@ -194,7 +194,7 @@ class FollowerQueryServiceImpl : FollowerQueryService {
             )
             .select { followers[Users.name] eq name and (followers[Users.domain] eq domain) }
             .map {
-                User.of(
+                userBuilder.of(
                     id = it[followers[Users.id]],
                     name = it[followers[Users.name]],
                     domain = it[followers[Users.domain]],
diff --git a/src/main/kotlin/dev/usbharu/hideout/service/user/UserServiceImpl.kt b/src/main/kotlin/dev/usbharu/hideout/service/user/UserServiceImpl.kt
index bb349ff3..6688ce48 100644
--- a/src/main/kotlin/dev/usbharu/hideout/service/user/UserServiceImpl.kt
+++ b/src/main/kotlin/dev/usbharu/hideout/service/user/UserServiceImpl.kt
@@ -21,6 +21,7 @@ class UserServiceImpl(
     private val apSendFollowService: APSendFollowService,
     private val userQueryService: UserQueryService,
     private val followerQueryService: FollowerQueryService,
+    private val userBuilder: User.UserBuilder,
     private val applicationConfig: ApplicationConfig
 ) :
     UserService {
@@ -35,7 +36,7 @@ class UserServiceImpl(
         val hashedPassword = userAuthService.hash(user.password)
         val keyPair = userAuthService.generateKeyPair()
         val userUrl = "${applicationConfig.url}/users/${user.name}"
-        val userEntity = User.of(
+        val userEntity = userBuilder.of(
             id = nextId,
             name = user.name,
             domain = applicationConfig.url.host,
@@ -57,7 +58,7 @@ class UserServiceImpl(
 
     override suspend fun createRemoteUser(user: RemoteUserCreateDto): User {
         val nextId = userRepository.nextId()
-        val userEntity = User.of(
+        val userEntity = userBuilder.of(
             id = nextId,
             name = user.name,
             domain = user.domain,