To provide a system for improving convenience in the operability of a user, in the charging management of a cellular radio telephone employing a prepaid system.

The system is provided with at least a usage time purchasing means for receiving purchasing information including a charging ID and a purchasing time in response to a purchasing request signal from a user terminal device, and searching a database on the basis of the charging ID and adding the purchasing time to a usable time of the corresponding charging management information; and a usable time monitoring means for receiving a charging ID in response to a usage start request signal from a cellular radio telephone, measuring a usage time using a usage start date and time as a base point, searching the database on the basis of the inputted charging ID to obtain a usable time of corresponding charging management information, and adding the usage time to the accumulated usage time in the charging management information at each predetermined elapsed time to monitor the usable time.