Two-stroke internal combustion engine

A two-stroke internal combustion engine which is capable of minimizing the quantity of blow-by or the quantity of air-fuel mixture to be discharged without being utilized for the combustion, of improving the fuel consumption and power of the engine, of reducing the content of poisonous components in the exhaust gas, and of reducing the manufacturing cost, without extensively altering the conventional engine. A through-hole or a communication groove is provided at the skirt portion of a piston to thereby enabling a scavenging inlet port to be communicated with the crank chamber. In the descending stroke, combustion exhaust gas from the combustion actuating chamber is enabled to be introduced, via a scavenging outlet port provided at a downstream end of the scavenging passageway, into the scavenging passageway while closing the scavenging inlet port at the skirt portion of the piston. In synchronization with the descending stroke, an air-fuel mixture is subsequently introduced from the crank chamber, via the through-hole or the communication groove, into the scavenging passageway. The combustion exhaust gas in the scavenging passageway is introduced into the combustion actuating chamber prior to the introduction of air-fuel mixture.