To improve a compression rate of a reversible compressor by eliminating noise without remarkable deterioration in the image quality of an original signal.

A local differential noise processing unit 10 is provided with a differential signal local level extract processing section 1 that extracts M sets of proper bit levels from a differential signal of input signals in N bits (M<N), a filtering section 2 that filters an output of the differential signal local level extract processing section 1, and synthesis processing section 3 that combines an output of the filtering section 2 with the input signal. Before compressing the input signal by a reversible compressor, the local differential noise processing unit 10 consisting of the sections above is used to reduce noise.