Abstract: A balancer system for suppressing vibrations in an internal combustion engine for a motorcycle has pair of balancer shafts, and a pair of first and second primary counterbalances supported on the balancer shafts, respectively, for rotation about axes parallel to the crankshaft of the engine in ganged relation to the crankshaft at the same speed as and in the opposite direction to the crankshaft. The balancer shafts extend parallel to the crankshaft and are positioned one on each side of the crankshaft. The first and second primary counterbalances are rotatable about respective centers which are connected by a line passing through a substantially central portion of the crankshaft, the first and second primary counterbalances being rotatably supported on the balancer shafts near ends thereof, with the centers being spaced from the central portion of the crankshaft by substantially equal distances.