PURPOSE: To make optimum on-off timing securable as well as to prevent a prefiring phenomenon from occurring, by setting up a reed valve at the downstream of a rotary valve on a suction passage of a two-cycle engine, free of housing at will.

CONSTITUTION: At a suction passage 12 to be interconnected to a crankcase 1 of a two-cycle engine E, there are provided with a reed valve 24, whose whole valve body rotates centering on a shaft 29 and a rotary valve 19 to be driven by the engine via a gear 21 at the upstream side. When the engine is driven at high speed, the reed valve 24 is housed inside a chamber 31 on the suction passage inner surface, thus a valve yoke forms an inner surface of the suction passage. Since the rotary valve 19 rotates synchronously with the engine, a compressed air-fuel mixture inside the crankcase 1 is in no case blown by to the suction passage 12. When the engine is driven at low speed, the reed valve 24 is situated as in an illustrated position, whereby at the time of an engine slow speed, such a weak point as being liable to produce a blow-by form the rotary valve 19 is eliminated.