An engine comprises: a V-belt type continuously variable transmission on one side of an engine case, said CVT being provided with and housing in a transmission case a drive pulley attached to one end of a crankshaft, a driven pulley attached to one end of a transmission shaft parallel to said crankshaft, a V-belt routed around the pulleys, said engine case supporting said crankshaft and transmission shaft in a rotatable manner, and a generator attached to the opposite end of said crankshaft in said engine case; in which a filter chamber is disposed in the opposite side surface of said transmission case of said engine case in a depressed manner so as to overlap with at least a part of said generator in the crankshaft direction, and an oil filter for filtering lubricating oil is disposed in said filter chamber.