1. A coding apparatus comprising: a first shift register for performing bit shifting on an input bit sequence and storing one bit of the input bit sequence after another; an input register for storing coefficients of terms on respective orders of a generator polynomial; and a logical operation section for obtaining logical products of the respective bits stored on the first shift register and associated bits stored on the input register and a logical product of each one bit input to the first shift register and an associated bit stored on the input register so that the earlier a bit of the input bit sequence was input, the higher-order one of the coefficients in the terms of the polynomial the input bit is associated with; deriving an exclusive logical sum of the logical products obtained; and then outputting the sum as one bit of a code sequence.