The invention provides a control system for preventing engine stall due to slippage of a wheel during propulsion in a fixed mode in which an engine and the wheel are rotated at a fixed ratio. When a wheel slips in a first mode in which an engine and the wheel are rotated at a predetermined ratio, an operating mode is shifted to a second mode in which a torque transmission between the engine and the wheel is interrupted and the vehicle is propelled by torque of driving machine connected to the wheel, or to a third mode in which the vehicle is propelled by delivering torque of the engine to thewheel while establishing a reaction torque by a predetermined rotary member.