An engine includes a balancer shaft that is supported at its both ends through bearings disposed within an engine crankcase. The balancer shaft lies generally parallel with a crankshaft and includes balancer weights, which are provided generally at the ends of the balancer shaft. At least one of the balancer weights is made up of first and second weight portions. The first and second weight portions are disposed on opposite sides of the corresponding bearing. In this manner, the bending moment on the shaft is reduced and, consequently, the balancer shaft can have a smaller diameter to reduce the size of the crankcase.