The present invention relates to an engine having an engine case (22) on one side of which a V-belt type of continuously variable transmission (CVT) is provided, said CVT (16) being placed in a transmission case (45) and constituted that a V-belt (57) is routed around a drive pulley (55) and a driven pulley (56), said drive pulley being attached to one end of a crankshaft (28), said driven pulley being attached to one end of a transmission shaft parallel to said crankshaft (28), wherein said crankshaft (28) is supported for free rotation with said engine case, one end of said crankshaft is projected from said engine case into said transmission case (45), said drive pulley is attached to said projected portion, and said transmission case (45) is made as a component separate from or independent of said engine case and supported with said engine case (22) so that a space (a) is present between said engine case and said transmission case (45), and wherein said transmission case (45) is provided with an inlet (45e) for introducing air inward and outlets (45f,45g) for discharging air outward, with said outlets open and directed toward the space (a) between said transmission case (45) and said engine case (22).