WORKING-GAS-CIRCULATION-TYPE ENGINE

A working gas circulation type engine (1) includes a combustion chamber (11) in which a working gas (Ar) having a ratio of specific heats higher than that of air can be expanded by combustion of a fuel (H 2 ), a circulation path (20) capable of circulating a gas containing the working gas (Ar) from a gas exhaust side to a gas suction side of the combustion chamber (11) and supplying the gas containing the working gas (Ar) to the combustion chamber (11) again, and a control device (60) that changes a control parameter for controlling the combustion of the fuel (H 2 ) based on a ratio of specific heats of the gas circulating in the circulation path (20). Therefore, there can be provided the working gas circulation type engine (1) capable of obtaining a stable output.