d 6 m 1 d 7 m 2 d 8 m 3 d 9 m 4 not shown in table 1 here u201c i u201d represents a bit position an exclusive or circuit 14 calculates an exclusive or of one of the mask patterns stored in the memory 12 and the output from the hard decision circuit 10 an output from the exclusive or circuit 14 is supplied to a checksum calculator 16 the calculator 16 calculates 16 checksums for each of 5 bits of d 1 to d 5 80 checksums in total among 10 bit information data d 0 to d 9 a majority decision unit 18 decides a majority of the 80 checksums output from the checksum calculator 16 to decode bits d 1 u2032 to d 5 u2032 corresponding to the orthogonal codes c 1 to c 5 to be more specific concerning the checksum it is decided to be 0 if 0 is majority and 1 if 1 is majority an orthogonal code multiplier 20 multiplies 5 bit data d 1 u2032 to d 5 u2032 by the orthogonal codes an exclusive or circuit 22 calculates an exclusive or of the exclusive or output from the exclusive or circuit 14 and the output from the orthogonal code multiplier 20 a majority decision unit 24 decides a majority of the exclusive or output from the exclusive or circuit 22 to decode bit d 0 u2032 to be more specific concerning the exclusive or it is decided to be 0 if 0 is majority and 1 if 1 is majority when the bit d 0 u2032 of the information data is determined by the majority decision unit 24 bits d 6 u2032 to d 9 u2032 of the information data can be determined based on the mask.