A power storage system controls a charging mode in which an assembled battery including a plurality of battery modules is charged. The assembled battery is charged through a constant current control based on a predetermined current value in the beginning of the charging mode and is charged through a constant voltage in the end of the charging mode. A determination part determines whether an apparatus electrically connected to an electric power line which the power storage system is electrically connected is in active. A controlling part constantly controls the current value for charging the assembled battery in the charging mode. In a case where the determination part determines that the apparatus is not in active, the controlling part sets the constant current value to a first current value at the beginning of a time period in which the charging mode is performed. In a case where the determination part determines that the apparatus is in active, the controlling part sets the constant current value to a second current value lower than the first current value in the beginning of the time period.