A power unit includes a transmission mechanism installed in a crankcase with a clutch apparatus for connecting and disconnecting the transmission of power between a crankshaft and the transmission mechanism being installed in a clutch chamber. An oil filter is set between an oil pump driven by the power transmitted from the crankshaft and portions to be supplied with oil is attached to a clutch cover. The provided power unit guarantees a certain degree of freedom in design for the size of the inner diameter of the cylinder bore, the location of the timing transmission mechanism, and the like. A smaller size of the power unit along the axial direction of the crankshaft needs to be achieved. The oil filter is disposed between the axis of the crankshaft and the axis of the clutch apparatus and below the axis of the crankshaft and the axis of the clutch apparatus.