To eliminate intermittent trouble in electrical appliances and machines, etc. occurring at switchover from nighttime power to inverter output in a nighttime power utilization power storage system designed to use nighttime power to charge and consume power during a daytime period.

In a nighttime power utilization power storage system provided with a timer 8 for utilizing nighttime power, a charger 10, a storage battery 11, a DC/AC inverter 13 for converting the stored nighttime power to usable power, and a switching relay 14 for switching between nighttime power and DC/AC inverter output, means is provided which starts up the DC/AC inverter in advance before power is switched from nighttime power to CD/AC inverter output. The means preferably has a "second switching relay 12" so that the switching relay 12 will be actuated before power is switched from nighttime power to DC/AC inverter output, thereby letting output of the storage battery flow into the DC/AC inverter to make it operable before the DC/AC inverter is started up.