Processor 23 calculates a first remainder, which is a remainder produced when an integral multiple data block is divided by a generator poly-nomial, by processing bits represented by the number of parallel bits in parallel. The integral multiple data block comprises bits positioned closer to the leading end of the input data than a final word which is a word at the tail end of the input data, in the case where a plurality of bits making up the input data are successively divided from the leading end with respect to each word which comprises the bits represented by the number of parallel bits. Processor 23 calculates a second remainder, which is a remainder produced when a final word valid data block made up of bits of the input data other than the integral multiple data block is divided by the generator polynomial. Processor 23 calculates an input data remainder, which is a remainder produced when the input data are divided by the generator polynomial, based on the first remainder and the second remainder.
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