To eliminate the need for a special midnight power measuring circuit and to allow change of integrated amount, reply for the energy amount at integration, etc., by a carrier wave control function which is superposed on a power line by a power supplier.

Conventional general power circuit is not discriminated from a midnight power circuit and the same circuit is shared for rationalization of duplicated instruments, wiring work, and charge management, etc. To allow sharing of the same circuit, a time-zone charge factor change function is provided and a timer function 9 is interlocked for measurement with a single system while a carrier wave control function 14 provided at a power supplier is allowed for power measurement through the power line.