A balancer device for an internal combustion engine includes upper and lower housings made of aluminum alloy. The upper housing includes a leg part fixed to the engine. The lower housing is coupled to the upper housing by tightening bolts. A pair of balancer shafts are rotatably supported by the upper and lower housings. A positioning pin is disposed at a distal end portion of the leg part for positioning the upper housing with respect to the engine by positional correspondence to a positioning hole of the engine when the tightening bolts are tightened. The leg part is inclined outwardly with respect to a body of the upper housing such that a distal end of the positioning pin is located outside of a proximal end of the leg part with respect to the body of the upper housing when the tightening bolts are loosened.