diff --git a/build.sbt b/build.sbt
index 5948dfb..564a33a 100644
--- a/build.sbt
+++ b/build.sbt
@@ -1,5 +1,3 @@
-import scala.collection.Seq
-
 ThisBuild / version := "0.1.0-SNAPSHOT"
 
 ThisBuild / scalaVersion := "3.3.1"
@@ -16,4 +14,4 @@ libraryDependencies ++= Seq(
   "com.squareup.okhttp3" % "okhttp" % "4.12.0",
   "com.typesafe" % "config" % "1.4.3",
   "ch.qos.logback" % "logback-classic" % "1.5.18"
-)
\ No newline at end of file
+)
diff --git a/src/main/scala/jp/co/dwango/urlslistmaker/Message.scala b/src/main/scala/jp/co/dwango/urlslistmaker/Message.scala
index 3ee585e..46cdf4f 100644
--- a/src/main/scala/jp/co/dwango/urlslistmaker/Message.scala
+++ b/src/main/scala/jp/co/dwango/urlslistmaker/Message.scala
@@ -1,12 +1,12 @@
 package jp.co.dwango.urlslistmaker
 
-trait Message
+sealed trait Message
 
 sealed trait SupervisorMessage extends Message
 case object Start extends SupervisorMessage
 case object Finished extends SupervisorMessage
-case class DownloadSuccess() extends SupervisorMessage
-case class DownloadFailure() extends SupervisorMessage
+case object DownloadSuccess extends SupervisorMessage
+case object DownloadFailure extends SupervisorMessage
 
 sealed trait UrlsFileLoaderMessage extends Message
 case object LoadUrlsFile extends UrlsFileLoaderMessage
@@ -14,4 +14,4 @@ case object LoadUrlsFile extends UrlsFileLoaderMessage
 sealed trait WebPageLoaderMessage extends Message
 
 case class WebPageUrl(domain: String)
-  extends WebPageLoaderMessage with SupervisorMessage
+  extends WebPageLoaderMessage, SupervisorMessage
diff --git a/src/main/scala/jp/co/dwango/urlslistmaker/Supervisor.scala b/src/main/scala/jp/co/dwango/urlslistmaker/Supervisor.scala
index ed0be0e..d214c66 100644
--- a/src/main/scala/jp/co/dwango/urlslistmaker/Supervisor.scala
+++ b/src/main/scala/jp/co/dwango/urlslistmaker/Supervisor.scala
@@ -56,12 +56,12 @@ object Supervisor:
           router ! url
           Behaviors.same
 
-        case DownloadSuccess() =>
+        case DownloadSuccess =>
           successCount += 1
           logAndCheckFinish()
           Behaviors.same
 
-        case DownloadFailure() =>
+        case DownloadFailure =>
           failureCount += 1
           logAndCheckFinish()
           Behaviors.same
diff --git a/src/main/scala/jp/co/dwango/urlslistmaker/WebPageLoader.scala b/src/main/scala/jp/co/dwango/urlslistmaker/WebPageLoader.scala
index dd2326d..0d12e6e 100644
--- a/src/main/scala/jp/co/dwango/urlslistmaker/WebPageLoader.scala
+++ b/src/main/scala/jp/co/dwango/urlslistmaker/WebPageLoader.scala
@@ -32,7 +32,7 @@ object WebPageLoader:
 
           client.newCall(request).enqueue(new Callback:
             override def onFailure(call: Call, e: IOException): Unit =
-              supervisor ! DownloadFailure()          // 通信自体が失敗
+              supervisor ! DownloadFailure          // 通信自体が失敗
 
             override def onResponse(call: Call, response: Response): Unit =
               try
@@ -49,10 +49,10 @@ object WebPageLoader:
                       StandardOpenOption.APPEND
                     )
                   match
-                    case Success(_) => supervisor ! DownloadSuccess()
-                    case Failure(_) => supervisor ! DownloadFailure()  // 書き込み失敗
+                    case Success(_) => supervisor ! DownloadSuccess
+                    case Failure(_) => supervisor ! DownloadFailure  // 書き込み失敗
                 else
-                  supervisor ! DownloadFailure()      // HTTP ステータスが失敗
+                  supervisor ! DownloadFailure      // HTTP ステータスが失敗
               finally
                 response.close()
           )