To improve the durability of an oil pump and prevent the deterioration of oil by forming a cooling water jacket on an oil pump fixed to a cover for covering a flywheel magnet, and passing cooling water in this cooling water jacket.

A cooling water jacket 60a is formed on an oil pump case 60 fixed to a cover 53 close to a flywheel magnet. Cooling water is passed through the cooling water jacket 60a, whereby an oil pump 57 itself housed in the oil pump case 60 is directly cooled with the cooling water. According to this structure, since the oil pump 57 itself is cooled even if the heat from the cover 53 is conducted, the oil pump 57 is hardly laid in high temperature state. Accordingly, the durability of the oil pump 57 is improved. Further, since the oil is hardly generate bubbles, the oil is hardly deteriorated.