A tensioner for applying tension to a balancer drive chain is mounted in a balancer housing which accommodates balancer shafts. Oil is supplied from a reservoir chamber to the tensioner. An oil jet member for lubricating the balancer drive chain is mounted at a position downstream in an oil flow direction from the reservoir chamber. Therefore, while enabling foreign matter contained in the oil to be discharged from the oil jet member without being accumulated within the tensioner, a predetermined pressure can be maintained in the reservoir chamber by a resistance to the flow of oil passing through the oil jet member. Also, a constriction is provided between the reservoir chamber and the oil jet member. Therefore, it is difficult for the oil to flow out of the reservoir chamber even after stoppage of an engine, thereby supplying the oil to the tensioner upon the next start of the engine without delay. Thus, it is possible to prevent the foreign matter from entering the tensioner for the balancer drive chain.