Combined power generation system

A combined power generation system (1) of the present invention is provided with: a gas fuel device (20, 71); a storage tank (22) for storing a liquefied fuel gas; a fuel supply pipe (24) that connects the storage tank (22) and the gas fuel device (20, 71) with each other and supplies a fuel gas, which is obtained by vaporizing the liquefied fuel gas, to the gas fuel device (20, 71); an exhaust pipe (29) for discharging an exhaust gas from the gas fuel device (20, 71); a Stirling engine (8) that is configured of a cylinder (9) and a piston (10); and a low temperature-side heat exchanger (11) that is provided on the fuel supply pipe (24) and performs heat exchange between the liquefied fuel gas, which serves as a cold heat source, and a low temperature-side working gas of the cylinder (9).