PURPOSE: To correspond to the time of insufficient sunshine and service interruption in the night by detaching a system when the service interruption of a system is detected and operating the system by a solar cell and a secondary battery.

CONSTITUTION: An output from a solar cell 1 is converted into ACs by an inverter 10, and the AC output is linked as phase is conformed to the system 15 side while being followed up to the maximum output of the solar cell 1. A secondary battery 6 for backup is charged at the time of normality while being linked with the system 15 at that time, the system 15 is disconnected when the power of the system 15 is cut off, and the reverse power flow of the system 15- is prevented while the operation of the inverter 10 is changed over to a fixed voltage-fixed frequency type from a maximum power tracking type, and the secondary battery 6 is changed over to a chargeable and dischargeable state simultaneously and operation by the solar cell 1 and the secondary battery 6 is performed. Consequently, the operation of the inverter 10 at the time of service interruption is stabilized and a power supply is ensured even at the time of the service interruption of the system 15. Accordingly, the title system can correspond to the time of insufficient sunshine and service interruption in the night.