A power generation system includes a first on-off valve that, with respect to a maintenance target device including at least one of a circulation pump, an evaporator, an expander, and a condenser in a medium circuit through which a medium with a boiling point lower than that of water circulates, is on an upstream side in a flow direction of the medium in the medium circuit, and is capable of shutting off the flow of the medium; a second on-off valve that is on a downstream side in the flow direction of the medium in the medium circuit, and is capable of shutting off the flow of the medium; a port that is communicable with the medium circuit between the first on-off valve and the second on-off valve; and a third on-off valve that is in the port.