A user, in requesting a service provider to provide predetermined service, sends to a service provider data and signature data created based upon the data. The service provider calculates a fee based upon this data and requests a bank to collect the fee from the user. The bank informs the user of the fee requested from the service provider. When the user protests the amount of the fee, the service provider discloses the data and signature data received from the user to the bank and when the bank judges based upon this signature data that this data is valid, it calculates a proper fee based upon this data and collects it from the user. As described above, it is enabled to collect a proper fee for service.