A standalone direct current (DC) power supplying system, which is not connected to commercial power, includes a power conditioner that supplies generated power W2 of a power generator to a DC bus, DC/DC converters that convert a bus voltage Vbs and supply load power (WLa+WLb) to load appliances, bidirectional DC/DC converters that supply a constant DC current from the DC bus to storage batteries or from the storage batteries to the DC bus, and an energy management system. When the generated power W2 exceeds the load power (WLa+WLb), the energy management system causes the converters to supply a constant DC current with a common charging rate to the storage batteries, and when the generated power W2 falls below the load power (WLa+WLb), the energy management system causes the converters to supply a constant DC current with a common discharging rate from the storage batteries to the DC bus.