PURPOSE: To provide sufficient disturbing operation even when a combustion chamber has a large space, to eliminate a need for a gas passage for boosting, and to sufficiently ensure a injecting gas weight.

CONSTITUTION: A valve seat 5 of an exhaust valve 3 forms a moving type and a boosting chamber 8 is arranged in a position to surround the back, on the outer peripheral side of the valve seat 5, of a cylinder head 1. Gas in a combustion chamber 2 is caused to flow in the boosting chamber 8 and gas (air) is boosted by means of a pressure on the exhaust valve 3 at the initial stage of combustion, and a plurality of gas injection nozzles 9 are formed in the position, fronting on the combustion chamber 2 at the periphery of the valve seat 5, of the cylinder head 1. High disturbing operation is exerted on the combustion chamber 2 through constitution wherein gas boosted in the boosting chamber 8 is injected in the combustion chamber 2 through the gas injection nozzles 9.