PURPOSE: To reduce entropy and to reduce a compression ratio by allocating a shortest code length when all the output of difference quantizers is 'zero'.

CONSTITUTION: Sub-band division is performed respectively and independently for three kinds of data, luminance signals Y and two kinds of color difference signals U and V. Sub-band division output is the size of the high frequency components of the respective signals, and when the quantized output of the luminance signals Y is 'zero', a probability that the quantized output of the color difference signals U and the quantized output of the color difference signals V are also 'zero' is high. Thus, when all the respective quantized output of the signals Y, U and V is 'zero', the shortest code length is allocated in entropy encoding. That is, when all the output of the quantizers 74, 75, 78', 96 of three signals Y, U and V is 'zero', the shortest range bit is allocated. In this case, in order to indicate the three pieces of the data of the signals Y, U and V, they are indicated in the form of zero run length/range when three pieces of the data are arrayed.