Abstract: An engine (10) that jets out combustion gas as a driving force is provided. The engine (10) includes a combustion chamber (11), a fuel supplying path (13) that mixes fuel and air and supplies to the combustion chamber (11), an igniter (42) that ignites the mixed gas in the combustion chamber (11), a gas ejecting path (15) that ejects combustion gas (51) from the combustion chamber (11) though a nozzle (18a); and an opening-closing apparatus (80) that opens and closes the gas ejecting path (15). The gas ejecting path (15) is opened by the opening-closing apparatus (80) immediately before ignition, simultaneously with ignition, or immediately after ignition.