An engine has a cylinder block having a vertical array of cylinders, a crankcase joined to one side of the cylinder block, a cylinder head joined to an opposite side of the cylinder block, pistons reciprocally movable in the cylinders, a crankshaft vertically extending through the engine block and rotatably supported in the cylinder block and the crankcase, the crankcase having couterweights, connecting rods interconnecting the pistons and the crankshaft, and a balancer mechanism coacting with the crankshaft. The balancer mechanism is disposed upwardly of the cylinder block and accommodated in a balancer housing projecting from upper surfaces of the cylinder block and the crankcase. The balancer mechanism comprises a driver gear mounted on the crankshaft, first and second balancer shafts extending parallel to the crankshaft, and first and second balancers mounted respectively on the first and second balancer shafts and operatively coupled to the driver gear. The first and second balancers are disposed on diametrically opposite sides of the driver gear and arranged such that a line interconnecting the centers of the first and second balancers is inclined with respect to an axis of the cylinder block.