An opening of an upper surface of an air cleaner main body has an air cleaner upper cover mounted thereon, and is closed by the air cleaner upper cover fastened by bolts via a seal member, and air cleaner bottom plates are fastened to the air cleaner main body via seal members in openings of a bottom surface of the air cleaner main body. Passage holes connecting an engine combustion chamber and the air cleaner main body are provided on the air cleaner bottom plates; and an opening of a front surface of the air cleaner main body is inserted into intake ducts of vehicle body frames via seal members, and configured as an air introduction port.