When both a position sensor and a motor malfunction, an ECU limits the engine rotation speed to such a speed range that the pressure inside a circulation route remains at or below a predetermined value even when the opening degree of a control valve is a minimum opening degree. When the position sensor is malfunction but the motor is not malfunction, the ECU relaxes the limits on the engine rotation speed, compared with when both the position sensor and the motor are malfunction, by driving the motor to an end of a motion range thereof and increasing the opening degree of the control valve to an opening degree larger than the minimum opening degree.