PURPOSE: To reduce oil temperature rise and power loss without agitating oil by forming an eccentric weight in such a way as to have an eccentric space inside and to have closed cylindrical outer face concentric with a balancer shaft, and supporting the balancer shaft in the state of the eccentric weight being submerged in lubricating oil.

CONSTITUTION: A balancer 30 is provided in a balancer chamber 10, and an eccentric weight 33 is provided with a space 34 eccentrically at the large diameter part integral with a balancer shaft 31. A cylinder 36 is fitted to the outer periphery of the large diameter part, and its end part is airtightly welded to form the balancer 30 with the cylindrical outer face. The balancer 30 is driven through a balancer drive gear 12 and a balancer driven gear 38 from a crankshaft 8, and a water pump shaft 41 is driven through gears 37, 51. The bearings 32L, 32R, 42, 43 of both shafts 31, 41 are lubricated with oil in the balancer chamber 10. The balancer 30 is rotated in the oil but rotated without agitating the oil because of its outer peripheral surface being the cylinder 36 of circular shape.