The left and right rear drive wheels of a vehicle are controlled independently, and the traveling direction of the vehicle is changed by providing a rotational speed difference between each of the left and right rear drive wheel. A vehicle operator merely designates the turning direction by moving an operation stick, e.g., to the left or right, which will in turn enable an automatic turn at an optimum curvature to be performed which frees the vehicle operator from complicated steering operations. A highly precise and responsive turn is achieved when the left and right independent control is implemented with a PLL control circuit.