diff --git a/README.md b/README.md
index 11c8c1b..c49008e 100644
--- a/README.md
+++ b/README.md
@@ -24,7 +24,7 @@ Add it in your root build.gradle at the end of repositories:
 
 ```groovy
     dependencies {
-        implementation 'com.github.studyplus:Studyplus-Android-SDK:2.5.1'
+        implementation 'com.github.studyplus:Studyplus-Android-SDK:2.5.2'
     }
 ```
 
@@ -41,12 +41,7 @@ Studyplus.instance.setup("consumer_key", "consumer_secret")
 Open an Activity to connect with Studyplus.
 
 ```kotlin
-try {
-    Studyplus.instance.startAuth(this@MainActivity, REQUEST_CODE_AUTH)
-} catch (e: ActivityNotFoundException) {
-    e.printStackTrace()
-    Toast.makeText(context, "Need for Studyplus 5.0.0+", Toast.LENGTH_LONG).show()
-}
+Studyplus.instance.startAuth(this@MainActivity, REQUEST_CODE_AUTH)
 ```
 
 Then save its result.
diff --git a/build.gradle b/build.gradle
index be51d5a..9ac676e 100644
--- a/build.gradle
+++ b/build.gradle
@@ -9,6 +9,8 @@ buildscript {
             'compileSdk'      : 28,
             'minSdk'          : 21,
             'targetSdk'       : 28,
+            'annotation'      : '1.1.0',
+            'core_ktx'        : '1.1.0',
             'appcompat'       : '1.1.0',
             'constraintLayout': '1.1.3'
     ]
diff --git a/studyplus-android-sdk/build.gradle b/studyplus-android-sdk/build.gradle
index 137f45a..0d5e856 100644
--- a/studyplus-android-sdk/build.gradle
+++ b/studyplus-android-sdk/build.gradle
@@ -44,7 +44,8 @@ dependencies {
     implementation "org.jetbrains.kotlinx:kotlinx-coroutines-core:$kotlin_cotoutines_version"
     implementation "org.jetbrains.kotlinx:kotlinx-coroutines-android:$kotlin_cotoutines_version"
 
-    implementation 'androidx.annotation:annotation:1.1.0'
+    implementation "androidx.annotation:annotation:$versions.annotation"
+    implementation "androidx.core:core-ktx:$versions.core_ktx"
 
     def okhttp = "3.14.2"
     implementation "com.squareup.okhttp3:okhttp:$okhttp"
diff --git a/studyplus-android-sdk/src/main/java/jp/studyplus/android/sdk/Studyplus.kt b/studyplus-android-sdk/src/main/java/jp/studyplus/android/sdk/Studyplus.kt
index eaf4d75..470d22c 100644
--- a/studyplus-android-sdk/src/main/java/jp/studyplus/android/sdk/Studyplus.kt
+++ b/studyplus-android-sdk/src/main/java/jp/studyplus/android/sdk/Studyplus.kt
@@ -40,9 +40,7 @@ class Studyplus private constructor() {
      * @since 2.0.0
      */
     fun startAuth(activity: Activity, requestCode: Int) {
-        if (consumerKey == null || consumerSecret == null) {
-            throw IllegalStateException("Please call setup method before this method call.")
-        }
+        check(consumerKey != null && consumerSecret != null) { "Please call setup method before this method call." }
 
         AuthTransit(consumerKey!!, consumerSecret!!).start(activity, requestCode)
     }
@@ -67,9 +65,7 @@ class Studyplus private constructor() {
      * @since 2.0.0
      */
     fun postRecord(context: Context, studyRecord: StudyRecord, listener: OnPostRecordListener?) {
-        if (!isAuthenticated(context)) {
-            throw IllegalStateException("Please check your application's authentication before this method call.")
-        }
+        check(isAuthenticated(context)) { "Please check your application's authentication before this method call." }
 
         runBlocking {
             try {
@@ -90,4 +86,4 @@ class Studyplus private constructor() {
         @JvmStatic
         val instance by lazy { Studyplus() }
     }
-}
\ No newline at end of file
+}
diff --git a/studyplus-android-sdk/src/main/java/jp/studyplus/android/sdk/internal/auth/AuthTransit.kt b/studyplus-android-sdk/src/main/java/jp/studyplus/android/sdk/internal/auth/AuthTransit.kt
index c3486aa..9fffb7d 100644
--- a/studyplus-android-sdk/src/main/java/jp/studyplus/android/sdk/internal/auth/AuthTransit.kt
+++ b/studyplus-android-sdk/src/main/java/jp/studyplus/android/sdk/internal/auth/AuthTransit.kt
@@ -1,8 +1,11 @@
 package jp.studyplus.android.sdk.internal.auth
 
 import android.app.Activity
+import android.content.Context
 import android.content.Intent
+import android.content.pm.PackageManager
 import android.net.Uri
+import androidx.core.net.toUri
 import jp.studyplus.android.sdk.R
 
 internal class AuthTransit
@@ -11,15 +14,23 @@ internal class AuthTransit
  * @param consumerSecret for API
  */
 constructor(
-        private val consumerKey: String,
-        private val consumerSecret: String
+    private val consumerKey: String,
+    private val consumerSecret: String
 ) {
     companion object {
         private const val EXTRA_CONSUMER_KEY = "consumer_key"
         private const val EXTRA_CONSUMER_SECRET = "consumer_secret"
+
+        private val URI_STORE = "market://details?id=jp.studyplus.android.app".toUri()
+        private val INTENT_STORE = Intent(Intent.ACTION_VIEW, URI_STORE)
     }
 
     fun start(activity: Activity, requestCode: Int) {
+        if (isInstalledStudyplus(activity).not()) {
+            openGooglePlayStore(activity)
+            return
+        }
+
         val intent = Intent()
         intent.action = Intent.ACTION_VIEW
         intent.putExtra(EXTRA_CONSUMER_KEY, consumerKey)
@@ -27,4 +38,13 @@ constructor(
         intent.data = Uri.parse(activity.getString(R.string.app_custom_scheme))
         activity.startActivityForResult(intent, requestCode)
     }
+
+    private fun openGooglePlayStore(context: Context) {
+        context.startActivity(INTENT_STORE)
+    }
+
+    private fun isInstalledStudyplus(context: Context): Boolean {
+        val packages = context.packageManager.getInstalledApplications(PackageManager.GET_META_DATA)
+        return packages.any { it.packageName == "jp.studyplus.android.app" }
+    }
 }
diff --git a/studyplus-android-sdk/src/main/res/values/strings.xml b/studyplus-android-sdk/src/main/res/values/strings.xml
index d23e36d..3d31321 100644
--- a/studyplus-android-sdk/src/main/res/values/strings.xml
+++ b/studyplus-android-sdk/src/main/res/values/strings.xml
@@ -1,3 +1,3 @@
 <resources>
-    <string name="app_custom_scheme">studyplus://auth/external/start</string>
+    <string name="app_custom_scheme" translatable="false">studyplus://auth/external/start</string>
 </resources>