An oil pan is provided below a crankcase of an engine. The oil pan has an oil reservoir in its upper case. An oil discharge pipe is located within the oil reservoir, the oil discharge pipe extending from an oil separator of a PCV system. The oil reservoir protrudes inward of an inner wall surface of a lower case. The oil reservoir has an oil drain hole on a bottom surface at its inwardly protruding portion. The oil reservoir communicates with a lower chamber through the oil drain hole.