A startup control method of controlling startup of a PV PCS 150 configured to perform interconnected operation in which a PV 100 is interconnected to a grid 10 to supply power to a load 400: supplies power from independent operation output of the PV PCS 150 to a storage PCS 250 by an independent operation that does not interconnect the PV 100 to the grid 10 before starting the interconnected operation; measures the output power amount of the PV 100 or the PV PCS 150 when the power is supplied to the storage PCS 250; and stops the independent operation to start the interconnected operation when the measured output power amount is larger than a predetermined amount.