With regard to a construction that a fan 41 is provided at one side of an engine 1 and covered by a fan casing 45, and an air cleaner 30 is arranged near the fan casing 45 and at a side of a cylinder head 5 on which an intake port 5a is disposed, a suction port 31a communicated with the inside of the fan casing 45 is provided in a main body 31 of the air cleaner 30. A barrier 46 is provided at a position facing to the suction port 31a in the air cleaner 30. A wall standing toward the fan casing 45 and the cylinder head 5 is formed on the outer surface of the main body 31 of the air cleaner 30. An air intake part is provided on one of side surfaces of a cover body 32 of the air cleaner 30 and the cover body 32 is constructed to be an equilateral polygon. An intake pipe 31k communicating the air cleaner 30 with the intake port 5a of the cylinder head 5 is constructed integrally with a main body 31 of the air cleaner 30.