To provide a card authentication system using unissued IC card and being difficult to tamper a card.

This IC card authentication system comprises an IC card, an issue device issuing the IC card, and an authentication device identifying the correctness of the IC card. The IC card is provided with a ROM 135 recording a unique manufacture number, and a memory 134. The issue device is provided with a control part 112 and a digital signature creation part 115 reading the manufacture number stored in the IC card, preparing second information including the whole or parts of the manufacture number, and writing a digital signature formed by converting the signature of the second information using a signature key in the memory 134. The authentication device is provided with a control part 122 and an authentication part 125 reading the manufacture number and the digital signature form the ROM 135 and the memory 134, respectively, verifying the signature of the second information using the digital signature, the manufacture number, and a verification key corresponding to the signature key and authenticating the correctness of the IC card.