A power conversion system includes a power generating apparatus, an auxiliary generation device that consumes power, an auxiliary-devised power source, a secondary battery device chargeable and dischargeable with power generated by the power generating apparatus, a bilateral DC/AC inverter that causes the power generating apparatus to cooperate with a commercial AC power source, and a switch unit provided between the commercial AC power source and the bilateral DC/AC inverter, DC terminals of the bilateral DC/AC inverter and an input of the auxiliary-devised power source, when the power generating apparatus generates no power, the switch unit is opened, the bilateral DC/AC inverter is stopped, and the voltage supplied from the secondary battery device to the auxiliary-devised power source is lower than that supplied from the secondary battery device to the auxiliary-devised power source when the power generating apparatus generates power.