The battery charging of electric vehicles, etc. is controlled so that the impact on the electric power system is lightened even when a lot of electric vehicles, etc. start the charging all at once. A device for controlling an electricity storage device installed in an electric vehicle or the like calculates a voltage drop by applying a load current at the time of performing the charging of the electricity storage device, and limits the charging quantity of the storage battery (installed in the electric vehicle or the like) based on the calculated voltage drop so that the voltage drop of the electric power system remains less than a prescribed level. Consequently, it becomes possible to reduce the voltage fluctuation around each of the electric vehicles, etc. that is about to execute the charging in cases where a lot of electric vehicles, etc. start the charging all at once.