To eliminate a temperature difference caused between combustion gas and working gas by performing combustion of fuel in a Stirling engine within a cylinder to develop a Stirling engine with high heat efficiency.

The Stirling engine is configured to directly heat working gas composed of air and combustion gas by heating air which is substantially isothermally compressed while cooling by being passed through a regenerative heat exchanger followed by force-feeding to a high-temperature cylinder, injecting fuel into the high-temperature cylinder to burn the fuel, and pushing down a piston by heating and expanding the working gas to take out a power. Prior to exhaust of the expanded working gas, the residual heat of the working gas is recovered and stored in the regenerative heat exchanger, and this heat is used to heat the substantially isothermally compressed air in the next cycle, thus improving the heat efficiency.