PURPOSE: To prevent a breakage piece from being sucked into a cylinder so as to prevent breakage of an engine itself by regulating the dislocating state of a fixing member of an inlet side lead valve by a part of a lead valve support member when a stopper for the valve is fixed to a cylinder.

CONSTITUTION: An inlet side lead valve is superposed on the inside of a suction hole of a lead valve support member 82 so as to function as the so-called check valve. An inlet side valve stopper 87 is screwed and fixed on a recess part 86 of a cylinder 71 by a fixing screw 871. The inlet side valve stopper 87 regulates the lift of the inlet side lead valve when the valve is opened. Though a recess part for fixing the head of the fixing screw 871 is formed on the back of the lead valve support member 82, in the fixing screw 871 mounting state, the distance from the screw head of the fixing screw 871 to the recess part is made smaller than the stem length of the fixing screw 871, so that the dislocating state of the fixing screw 871 can be prevented. Accordingly, it is possible to prevent breakage of an engine due to fallout of a screw.