A first information processing unit 100 stores identification information into a storage module 152, stores an encrypted contents signal into a mass storage unit 180, and supplies the encrypted contents signal and identification information to a second information processing unit 200 through a communication section 110. In a receiving unit 170 of the first information processing unit 100, log information generated by a purchase processing module 153 is stored into the storage module 152 every time the contents key is decoded, and the log information is transmitted at predetermined timing to a key management center 30 through the transmission section 110. The second information processing unit 200 receives the encrypted contents signal and the identification information through a communication section 210, and causes a contents processing section 260 to decode the encrypted contents signal and to append the identification information thereto.