A Stirling engine includes a high-temperature side cylinder and an expansion piston that is subjected to gas lubrication, or more specifically static pressure gas lubrication, relative to the high-temperature side cylinder and has a layer on an outer peripheral surface thereof, the layer being formed from a flexible material having a higher linear expansion coefficient than a base material of the expansion piston, wherein a booster pump and a ECU are provided as a contact avoiding device to prevent the expansion piston from contacting the high-temperature side cylinder when an engine operation is stopped until a temperature of the expansion piston can be suppressed below a predetermined value.