A traction controlling apparatus is configured such that if a slip of a driving wheel is detected, then a throttle valve opening is reduced to a first predetermined value. If failure is detected while the throttle valve opening is reduced to the first predetermined value, then the throttle valve opening is further reduced to a second predetermined value. If the acceleration grip is manipulated to a fully closed position while the throttle valve opening is reduced to the second predetermined value, then the control is ended and throttle control by a direct manipulation of the acceleration grip is enabled.