Provided is a power supply system comprising: distributed energy resources (2) connected to a power line (L1) for feeding power from a commercial power system (10) to an important load (30); a switch (3) provided in the power line (L1) for opening and closing the power line (L1); an impedance element (4) connected in parallel to the switch (3) in the power line (L1); a voltage detection unit (5) for detecting a voltage on the commercial power system (10) side with respect to the switch (3); and a control unit (6) for releasing, when a voltage detected by the voltage detection unit (5) becomes equal to or lower than a set point, the switch (3) such that the distributed energy resources (2) and the commercial power system (10) are connected through the impedance element (4), and the distributed energy resources (2) continue operation including reverse power flow.