diff --git a/lib/debug/session.rb b/lib/debug/session.rb
index 0075231e3..668afa37a 100644
--- a/lib/debug/session.rb
+++ b/lib/debug/session.rb
@@ -2080,22 +2080,27 @@ def self.info msg
     log :INFO, msg
   end
 
-  def self.debug msg
-    log :DEBUG, msg
-  end
-
-  def self.log level, msg
-    @logfile = STDERR unless defined? @logfile
-
+  def self.check_loglevel level
     lv = LOG_LEVELS[level]
     config_lv = LOG_LEVELS[CONFIG[:log_level] || :WARN]
+    lv <= config_lv
+  end
 
-    if defined? SESSION
-      pi = SESSION.process_info
-      process_info = pi ? "[#{pi}]" : nil
+  def self.debug(&b)
+    if check_loglevel :DEBUG
+      log :DEBUG, b.call
     end
+  end
+
+  def self.log level, msg
+    if check_loglevel level
+      @logfile = STDERR unless defined? @logfile
+
+      if defined? SESSION
+        pi = SESSION.process_info
+        process_info = pi ? "[#{pi}]" : nil
+      end
 
-    if lv <= config_lv
       if level == :WARN
         # :WARN on debugger is general information
         @logfile.puts "DEBUGGER#{process_info}: #{msg}"
diff --git a/lib/debug/thread_client.rb b/lib/debug/thread_client.rb
index 4e526bde0..b194edda9 100644
--- a/lib/debug/thread_client.rb
+++ b/lib/debug/thread_client.rb
@@ -1057,22 +1057,30 @@ def wait_next_action_
     end
 
     def debug_event(ev, args)
-      args = args.map { |arg| DEBUGGER__.safe_inspect(arg) }
-      DEBUGGER__.debug("#{inspect} sends Event { type: #{ev.inspect}, args: #{args} } to Session")
+      DEBUGGER__.debug{
+        args = args.map { |arg| DEBUGGER__.safe_inspect(arg) }
+        "#{inspect} sends Event { type: #{ev.inspect}, args: #{args} } to Session"
+      }
     end
 
     def debug_mode(old_mode, new_mode)
-      DEBUGGER__.debug("#{inspect} changes mode (#{old_mode} -> #{new_mode})")
+      DEBUGGER__.debug{
+        "#{inspect} changes mode (#{old_mode} -> #{new_mode})"
+      }
     end
 
     def debug_cmd(cmds)
-      cmd, *args = *cmds
-      args = args.map { |arg| DEBUGGER__.safe_inspect(arg) }
-      DEBUGGER__.debug("#{inspect} receives Cmd { type: #{cmd.inspect}, args: #{args} } from Session")
+      DEBUGGER__.debug{
+        cmd, *args = *cmds
+        args = args.map { |arg| DEBUGGER__.safe_inspect(arg) }
+        "#{inspect} receives Cmd { type: #{cmd.inspect}, args: #{args} } from Session"
+      }
     end
 
     def debug_suspend(event)
-      DEBUGGER__.debug("#{inspect} is suspended for #{event.inspect}")
+      DEBUGGER__.debug{
+        "#{inspect} is suspended for #{event.inspect}"
+      }
     end
 
     class Recorder