A CD-ROM is recorded with a CD-ROM effective period and an effective period of a content stored in the CD-ROM. A CD-ROM effective period judging section of a personal computer reads the effective periods, compares these periods with a machine date generated by a machine date generating section and enables a purchase slip transmitting section to transmit a purchase slip only when the machine data falls within the effective periods. A CD-ROM effective period judging section of a center compares the present date with the CD-ROM effective period and the content effective period registered on a goods master, reads the key from the goods master and transmits the key to the personal computer only when both of a CD-ROM number and a content ID written onto the received purchase slip fall within the effective periods.