A region specifying unit specifies a first region where a regular bit string is in a transmission frame, a second region which has a bit string similar to a defined bit string, and a third region which has a non-regular bit string and extracts a difference between the bit string in the second region and the defined bit string. A first CRC acquisition unit acquires a first CRC corresponding to the regular bit string. A second CRC acquisition unit acquires a second CRC corresponding to the defined bit string. A differential CRC acquisition unit acquires a differential CRC corresponding to the extracted difference. A third CRC generation unit generates a third CRC corresponding to a bit string in the third region. A frame CRC generation unit generates a CRC of the transmission frame using the first CRC, the second CRC, the differential CRC, and the third CRC.