PURPOSE: To dispense with the remodelling of an engine body and prevent a lubricating pump from damage caused by casting sand and lubricating oil from early degradation in additionally providing a filter cartridge.

CONSTITUTION: An engine E is provided in a cylinder head with an oil cooling chamber 7. A lubricating pump 3 and oil cooler 8 communicate respectively to the inlet side and the outlet side of the oil cooling chamber 7. An amount increasing oil pan is additionally provided on a body oil pan 10 of the engine E. The body oil pan 10 communicates to the volume increasing oil pan through a return oil path 15, while the lubricating pump 3 communicates to a strainer oil suction port 22 of the volume increasing oil pan through an oil suction path 13. A filter cartridge 30 is additionally provided in the volume increasing oil pan to return oil Oi from the oil cooler 8 through a filter cartridge 30 from an external return oil path 18 into the volume increasing oil pan.