PURPOSE: To read a channel code accurately without being affected by low frequency noise by discriminating channel bits of a prescribed number only to be '1' in the order of higher likelihood among channel bits of an inputted channel code.

CONSTITUTION: An additional code generator 11 uses codes being the addition of low-order 3-bit 110 to 8-bit information words a1-a8 further as channel codes when number K of 1 included in the 8-bit information words a1-a8 is 2. In the case of K=3, the low-order 3-bit 110 is added and in the case of K=4, the low-order 3-bit 000 is added. Thus, the number of 1 included in a 11-bit channel code without fail is 4. A binarizing means 14 samples an inputted channel signal and the sample values are put in order in the order of larger values. The 1st to 4th samples are sampled, they are discriminated to be 1 and the rest is discriminated to be 0. Then the high-order 8-bit (b1-b8) is adopted to decode the code into the 8-bit information words a1-a8.