PURPOSE: To reduce a knocking phenomenon of a Diesel engine at its low speed revolution, by providing shock absorbing valves, which relax an impulsive sound and vibration of explosion at low speed revolution, to a cylinder head of the Diesel engine.

CONSTITUTION: A shock absorbing valve 1 operated at fixed pressure is mounted to a cylinder head 9 of a Diesel engine. The valve 1 is arranged such that tension of a spring 2 is a little larger than compressive pressure. If fuel is burned and exploded in a cylinder, high pressure of explosion gas is applied to the valve 1 to instantaneously press the spring 2 and partially absorb the explosion gas in a shock absorbing chamber 5. And then as pressure of the gas decreases, stored energy of the spring 2 is returned to the side of a piston 6 through the explosion gas. A fixing rod 3 is lowered at high speed revolution of the engine to fix the valve 1.