To provide a check code generation method and check code generation device capable of judging off-line that an IC card is a forged IC card, even when the forged IC card having completely copied data written into an authentic IC card including the check code is generated.

A data writing device 100 creates a check code A from a manufacturer serial number of an IC chip 2 and a data stored in an IC card 1 at a check code creation part 131, and writes the check code A together with stored data in the IC chip 2 after encrypting the check code A at an encryption part 132. A data reading device 200 creates the manufacturer serial number of the IC chip 2 and a check code B for checking based on the stored data at a check code generating part 203, and decodes the check code A at a decoding part 202. Then authenticity judgement is performed by checking matching/ non-matching between the check code A and the check code B at an authenticity judging part 204.