This power generation system is provided with a medium circuit, a circulation pump, an evaporator which evaporates a medium, an expander configured to be driven using the medium evaporated by the evaporator, a condenser configured to condense the medium discharged from the expander, a generator configured to be driven by the expander to generate power, a cooling system configured to cool the generator using the medium taken out from the medium circuit at a downstream side of the condenser, and a gas-liquid separator configured to separate the medium heated as a consequence of cooling the generator by the cooling system into gas and liquid phases, wherein the gas phase of the medium is flowed into the medium circuit at an upstream side of the condenser, and the liquid phase of the medium is flowed into the medium circuit at the downstream side of the condenser.