To set a parameter of a filter while considering a state of encoding for every block within a macro block, when reducing quantization noise, such as, mosquito noise through the filter.

A mosquito noise filter module 200 performs smoothing processing for reducing mosquito noise on image data for every macro block outputted from an adder 175. A mosquito noise occurrence indicator generator 180 generates an occurrence indicator of mosquito noise, according to the state of encoding by each block within the macro block, on the basis of decoding information generated by a variable length decoder 110. In order to determine the state of encoding by each block, coded_block_pattern of MPEG-2 is referred to. Based on the generated mosquito noise occurrence indicator, a parameter setter 190 sets parameters for the mosquito noise filter module 200.