Abstract: A partition member divides the interior of the rear cylinder head into a low pressure chamber and a high pressure chamber on one side of the partition member facing the valve plate and into an oil separating chamber on the opposite side. Formed in the high pressure chamber at its peripheral portion are first and second oil collecting chambers which communicate with the drive shaft-fitted hole of the cylinder block, allowing lubricating oil therein to be fed to the hole. The oil separating chamber is provided with a guide wall for guiding suction fluid in a swirling manner. A third oil collecting chamber is defined between the guide wall and the inner peripheral wall of the rear cylinder head and communicates with the oil sump in the cylinder block, allowing lubricating oil therein to be returned to the oil sump.