To provide a service that makes a rate constant through the setting of a user or contact between enterprises independently of increase/decrease in traffic of a system.

The user can receive a service (service of a 1st service class) by which the user can make communication at a highest rate at all times depending on the setting or contact between enterprises. When traffic of the system is more than that required for this service, a service whose grade is decreased (service of 2nd service class) is conducted. Furthermore, the user can receive a service (service of a 3rd service class) by which the user can make communication at a low rate at all times depending on the setting or contact between enterprises. The user can make a request of enhancing quality of one communication in the case of a very important speech or the like. In this case, an extract charge is demanded on the user for the speech.