To provide a waiting power compensating circuit in which hindrance does not arise in the operating of an apparatus by compensating the waiting power, even when the power generation capacity of a solar cell drops due to the shortage of the luminous energy of irradiation in waiting condition.

A contact 8 of a relay Ry is interposed between a storage battery 6 which is charged by receiving the power supply from a solar cell 1, and a commercial power line 9. A microcomputer 3 detects that the voltage of the storage battery 6 has dropped to a prescribed value, operates the relay Ry, closes a contact 8, and charges the storage battery 6 from the commercial power line 9 via and setting this contact 8. Hereby, even if the condition that the luminous energy of irradiation runs short and the power generation capacity of the solar cell drops continues over long period, accumulation means is supplied with sufficient waiting power at all times, and it will not interfere with the action of an apparatus.