To provide a Stirling engine capable of taking OT countermeasures of catalyst provided on the downstream side more than the Stirling engine in an exhaust system of an internal combustion engine.

This Stirling engine 10 provided on the upstream side more than catalyst 300 provided in the exhaust system 100 of the internal combustion engine 200 is provided with a communicating passage 400 for communicating a heating device 47 with a cooling device 45 of the Stirling engine directly and a catalyst corresponding temperature acquiring means for acquiring catalyst corresponding temperature Ta corresponding to temperature T of the catalyst. When the catalyst corresponding temperature exceeds a predetermined value Tswitch, the heating device and the cooling device are directly and mutually communicated by the communicating passage. Working fluid passes by bypassing a regenerator 46 to reduce exhaust heat recovery efficiency of the Stirling engine and prevent excessive heating of the catalyst by reducing temperature of exhaust gas after passing through the Stirling engine.

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