diff --git a/lib/fluent/plugin/in_monitor_agent.rb b/lib/fluent/plugin/in_monitor_agent.rb
index a5edc5f5a7..8692e9de98 100644
--- a/lib/fluent/plugin/in_monitor_agent.rb
+++ b/lib/fluent/plugin/in_monitor_agent.rb
@@ -50,7 +50,7 @@ def initialize(server, agent)
 
       def do_GET(req, res)
         begin
-          code, header, body = process(req, res)
+          code, header, body = process(req)
         rescue
           code, header, body = render_json_error(500, {
               'message '=> 'Internal Server Error',
@@ -67,85 +67,69 @@ def do_GET(req, res)
         res.body = body
       end
 
-      def build_object(req, res)
+      def build_object(req)
         unless req.path_info == ""
           return render_json_error(404, "Not found")
         end
 
+        qs = Hash.new { |_, _| [] }
         # parse ?=query string
         if req.query_string
           begin
-            qs = CGI.parse(req.query_string)
+            qs.merge!(CGI.parse(req.query_string))
           rescue
             return render_json_error(400, "Invalid query string")
           end
-        else
-          qs = Hash.new {|h,k| [] }
         end
 
         # if ?debug=1 is set, set :with_debug_info for get_monitor_info
         # and :pretty_json for render_json_error
-        opts = {with_config: @agent.include_config, with_retry: @agent.include_retry}
-        if s = qs['debug'] and s[0]
+        opts = {}
+
+        if qs['debug'.freeze].first
           opts[:with_debug_info] = true
           opts[:pretty_json] = true
         end
 
-        if ivars = (qs['with_ivars'] || []).first
+        if ivars = qs['with_ivars'.freeze].first
           opts[:ivars] = ivars.split(',')
         end
 
-        if with_config = get_search_parameter(qs, 'with_config'.freeze)
+        if with_config = qs['with_config'.freeze].first
           opts[:with_config] = Fluent::Config.bool_value(with_config)
+        else
+          opts[:with_config] = @agent.include_config
         end
 
-        if with_retry = get_search_parameter(qs, 'with_retry'.freeze)
+        if with_retry = qs['with_retry'.freeze].first
           opts[:with_retry] = Fluent::Config.bool_value(with_retry)
+        else
+          opts[:with_retry] = @agent.include_retry
         end
 
-        if tag = get_search_parameter(qs, 'tag'.freeze)
+        if tag = qs['tag'.freeze].first
           # ?tag= to search an output plugin by match pattern
           if obj = @agent.plugin_info_by_tag(tag, opts)
             list = [obj]
           else
             list = []
           end
-
-        elsif plugin_id = get_search_parameter(qs, '@id'.freeze)
+        elsif plugin_id = (qs['@id'.freeze].first || qs['id'.freeze].first)
           # ?@id= to search a plugin by 'id <plugin_id>' config param
           if obj = @agent.plugin_info_by_id(plugin_id, opts)
             list = [obj]
           else
             list = []
           end
-
-        elsif plugin_id = get_search_parameter(qs, 'id'.freeze)
-          # Without @ version of ?@id= for backward compatibility
-          if obj = @agent.plugin_info_by_id(plugin_id, opts)
-            list = [obj]
-          else
-            list = []
-          end
-
-        elsif plugin_type = get_search_parameter(qs, '@type'.freeze)
+        elsif plugin_type = (qs['@type'.freeze].first || qs['type'.freeze].first)
           # ?@type= to search plugins by 'type <type>' config param
           list = @agent.plugins_info_by_type(plugin_type, opts)
-
-        elsif plugin_type = get_search_parameter(qs, 'type'.freeze)
-          # Without @ version of ?@type= for backward compatibility
-          list = @agent.plugins_info_by_type(plugin_type, opts)
-
         else
           # otherwise show all plugins
           list = @agent.plugins_info_all(opts)
         end
 
-        return list, opts
-      end
-
-      def get_search_parameter(qs, param_name)
-        return nil unless qs.has_key?(param_name)
-        qs[param_name].first
+        [list, opts]
       end
 
       def render_json(obj, opts={})
@@ -163,8 +147,8 @@ def render_json_error(code, obj, opts={})
     end
 
     class LTSVMonitorServlet < MonitorServlet
-      def process(req, res)
-        list, _opts = build_object(req, res)
+      def process(req)
+        list, _opts = build_object(req)
         return unless list
 
         normalized = JSON.parse(list.to_json)
@@ -186,8 +170,8 @@ def process(req, res)
     end
 
     class JSONMonitorServlet < MonitorServlet
-      def process(req, res)
-        list, opts = build_object(req, res)
+      def process(req)
+        list, opts = build_object(req)
         return unless list
 
         render_json({
@@ -197,7 +181,7 @@ def process(req, res)
     end
 
     class ConfigMonitorServlet < MonitorServlet
-      def build_object(req, res)
+      def build_object(req)
         {
           'pid' => Process.pid,
           'ppid' => Process.ppid
@@ -206,8 +190,8 @@ def build_object(req, res)
     end
 
     class LTSVConfigMonitorServlet < ConfigMonitorServlet
-      def process(req, res)
-        result = build_object(req, res)
+      def process(req)
+        result = build_object(req)
 
         row = []
         JSON.parse(result.to_json).each_pair { |k, v|
@@ -220,8 +204,8 @@ def process(req, res)
     end
 
     class JSONConfigMonitorServlet < ConfigMonitorServlet
-      def process(req, res)
-        result = build_object(req, res)
+      def process(req)
+        result = build_object(req)
         render_json(result)
       end
     end