PURPOSE: To obtain a smooth interpolation picture without solving simultaneous equations by executing interpolation through the use of a weighting filter executing smoothing at the time of generating the interpolation picture from a reproduction average value.

CONSTITUTION: An average value circuit 104, an average value quantizer 105, an average value inverse quantizer 106, an average value picture generation circuit 107 and an interpolation circuit 108 are provided. For generating the interpolation picture from the reproduction average value, interpolation is executed by using the weighting filter for smoothing. Namely, a weighting coefficient is changed by the position of the average value picture, filtering for the average value picture is simply repeated for plural times, filtering is executed for the whole positions of the average value picture. These operations are executed respectively in encoding and decoding. Thus, the smooth interpolation picture can be obtained without solving the complicated simultaneous equations.