Request information 3 is transmitted from a transmission means 1a of a communication device 1 to a server 2. Then, related information 4a corresponding to the request information 3 and an identification code 4b are obtained and transmitted to the communication device 1 by a transmission means 2c. The related information 4a and identification code 4b are stored in a storage means 1c of the communication device 1. Thereafter, purchase request information 5a is transmitted to the server 2 by the transmission means 1a. This purchase request information 5a is added with an identification code 5b and user identification information 5c. Then, content data 6a corresponding to the purchase request information 5a and additional data 6b corresponding to the identification code 5b are transmitted to the communication device 1 by the transmission means 2c of the server 2.