To prevent an unauthorized duplication and to surely limit the number of ulilization of contents data or the like.

A memory 53 stores hash values of contents management data. When an IEEE-1394 interface 51 certifies a personal computer being connected to the interface via a network 4, it transmits contents management data to the personal computer and also receives the hash data of the contents management data from the personal computer. When the interface 51 authenticates the personal computer, it judges the coincidence between the hash value of the received contents management data and the hash value of the stored contents management data.