Power transmitting device

A cam mechanism is provided with a forward rotation plate 46 and a reverse rotation plate 47. The respective plates 46 and 47 are urged by the respective coil springs 57a to 57f in the directions opposite to each other. When the number of rotations of the front wheels becomes great relative to the number of rotations of the rear wheels, the forward rotation plate 46 rotates. Thus, a main cam 32 which is urged by the respective coil springs 57a and 57d toward the neutral position rotates together with the forward rotation plate 46 when the forward rotation plate 46 rotates. When the number of rotations of the rear wheels becomes great relative to the number of rotations of the front wheels, the reverse rotation plate 47 rotates. Thus, the main cam 32 which is urged by the respective coil springs 57b, 57c, 57e and 57f toward the neutral position rotates together with the reverse rotation plate 47 when the reverse rotation plate 47 rotates.