A charging control device for an electricity storage system includes a unit to detect an electricity remaining amount of a battery, a unit to calculate a necessary charge amount, a unit to calculate a necessary charge period, and a unit to start a charging from a charger to the battery at a start timing of nighttime. The start timing is defined to go back by the necessary charge period from a target timing, when the charging is defined to be finished at the target timing. The necessary charge amount is necessary for a following daytime, and is discharged for a load in the daytime.