diff --git a/app/services/modbus/polling_service.rb b/app/services/modbus/polling_service.rb
index 710705f..37fce95 100644
--- a/app/services/modbus/polling_service.rb
+++ b/app/services/modbus/polling_service.rb
@@ -5,7 +5,7 @@ module Modbus
   class PollingService
     class << self
       def start
-        return if defined?(@scheduler) && @scheduler&.running?
+        return if defined?(@scheduler) && @scheduler.jobs.any?
 
         puts "[#{Time.current}] Modbus polling service 시작됨 (Rufus)"
         @scheduler = Rufus::Scheduler.new
@@ -20,12 +20,16 @@ module Modbus
       end
 
       def stop
-        @scheduler&.shutdown
-        puts "[#{Time.current}] Modbus polling service 중지됨"
+        if defined?(@scheduler)
+          @scheduler.shutdown(:kill)
+          puts "[#{Time.current}] Modbus polling service 중지됨"
+        else
+          puts "[#{Time.current}] Scheduler 인스턴스 없음"
+        end
       end
 
       def running?
-        @scheduler&.running?
+        defined?(@scheduler) && @scheduler.jobs.any?
       end
 
       private