To integrate a slide die of a die for cylinder, to simplify the structure of the die, and to reduce the manufacturing cost by forming paired exhaust passages in each side wall of a crank case and a cylinder, and forming a passage wall of a branched passage for the scavenge and air integrally with the cylinder approximately in parallel therewith.

An exhaust port 13a and a scavenging port 9 are mounted on a side part of a cylinder 2, an intake port 15a opened in the rising of a piston 4 for supplying the air-fuel mixture into a crank chamber 5a, and a scavenging passage 109d connected to the scavenging port 9 are respectively formed, and air for scavenging, supplied from an air cleaner 11 is supplied to the scavenging passage 109d. On this occasion, an insulator 30 provided with an air passage 10b and an air-fuel mixture passage 15b communicated with the intake port 15a, formed in parallel with each other, is mounted, and a check valve 16 for allowing only the air flow toward the scaventing passage 109d side is mounted at a side connected to the scavenging passage 109b of the air passage 10b, of the insulator 30. The branch passage 109e at both sides of the cylinder 2 is connected to the scavenging passage 109b.