A power unit including an internal combustion engine has an electric power generator mounted on an end of a crankshaft, a power transmitting member mounted on the other end of the crankshaft, and a lubricant oil filter. The oil filter partly overlaps the electric power generator as viewed in the direction of a crankshaft axis, and is positioned between the electric power generator and a crank weight on the crankshaft with respect to the direction of the crankshaft axis. The oil filter has a filter mount axis forming an acute angle to the crankshaft axis. The engine crankcase is thus prevented from bulging outwardly, and the power unit is reduced in size in its entirety.