To provide an improved air scavenging type two-cycle combustion engine equipped with a pressure reducing device in which clogging of a decompressing hole can easily be removed, a two-cycle combustion engine includes a delivery passage (32) for introducing air into a combustion chamber (9) prior to an air-fuel mixture. This delivery passage (32) has a downstream opening (32c) through which the air is introduced into the combustion chamber by way of a scavenging port (40a). A decompressing hole (38) is defined for communicating the combustion chamber (9) to a portion of the delivery passage (32) and is closed by a piston (16) then ascending, at a timing delayed relative to closure of an exhaust port (31).