diff --git a/README.rdoc b/README.rdoc
index cbac481..0a1718b 100644
--- a/README.rdoc
+++ b/README.rdoc
@@ -18,7 +18,8 @@ this sources folked 'fluent-plugin-redis'. (https://github.com/yuki24/fluent-plu
       timeout TIMEOUT(float, all , 5.0)
       key_prefix prefix_(string, all, '')
       key_suffix _suffix(string, all , '')
-      store_type zset(zset|set|list|string, all, zset)
+      store_type zset(zset|zincrby|set|list|string, all, zset)
+      increment_score zset(float, all, 1.0)
       key_name key(string, all, nil)
       score_name score(string, all , nil)
       value_name value(string, all, nill)
diff --git a/lib/fluent/plugin/out_redisstore.rb b/lib/fluent/plugin/out_redisstore.rb
index c9c87c0..3b6e897 100644
--- a/lib/fluent/plugin/out_redisstore.rb
+++ b/lib/fluent/plugin/out_redisstore.rb
@@ -23,6 +23,7 @@ def configure(conf)
       @key_name = conf['key_name']
       @fixed_key_value = conf.has_key?('fixed_key_value') ? conf['fixed_key_value'] : nil
       @score_name = conf['score_name']
+      @increment_score = conf.has_key?('increment_score') ? conf['increment_score'] : 1.0
       @value_name = conf['value_name']
       @key_expire = conf.has_key?('key_expire') ? conf['key_expire'].to_i : -1
       @value_expire = conf.has_key?('value_expire') ? conf['value_expire'].to_i : -1
@@ -54,6 +55,8 @@ def write(chunk)
                 (tag, record) = message
                 if @store_type == 'zset'
                   operation_for_zset(record)
+                elsif @store_type == 'zincrby'
+                  operation_for_zincrby(record)
                 elsif @store_type == 'set'
                   operation_for_set(record)
                 elsif @store_type == 'list'
@@ -100,6 +103,25 @@ def operation_for_zset(record)
       end
     end
 
+    def operation_for_zincrby(record)
+      if @fixed_key_value
+        k = @fixed_key_value
+      else
+        k = traverse(record, @key_name).to_s
+      end
+      v = traverse(record, @value_name)
+      sk = @key_prefix + k + @key_suffix
+      
+      @redis.zincrby sk , @increment_score, v
+      if @key_expire > 0
+        @redis.expire sk , @key_expire
+      end
+      if @value_length > 0
+        script = generate_zremrangebyrank_script(sk, @value_length, @order)
+        @redis.eval script
+      end
+    end
+
     def operation_for_set(record)
       if @fixed_key_value
         k = @fixed_key_value