A balancer integrated with a crankcase of an internal combustion engine, including balance shafts that are driven and rotated by a rotational force transmitted from a crankshaft of the internal combustion engine to the balance shafts through an endless transmission member to reduce second order vibration of the internal combustion engine, a tensioner that applies tension to the endless transmission member by pressing an outer surface of the endless transmission member using a hydraulic pressure, a tensioner mounting portion to which the tensioner is mounted, the tensioner mounting portion being integrally formed with the crankcase, and an oil supply portion projectingly disposed along an outer surface of the tensioner mounting portion and integrally formed with the tensioner mounting portion, the oil supply portion supplying the hydraulic pressure to the tensioner through the tensioner mounting portion.