A variable valve timing mechanism 9 includes an electric motor 10 coupled to an intake camshaft 7. A plurality of rotation sensors 18 to 20 are located about the rotor 17 of the electric motor 10. Each of the sensors 18 to 20 outputs a signal corresponding to induced voltage generated by rotation of the rotor 17. Based on the signals form the rotation sensors 18 to 20, reverse rotation of an engine is detected. A counter C is decremented every time a crank signal is output after the occurrence of reverse rotation is detected. Further, a subtraction value Y is computed that corresponds to a discrepancy between the counter C and the actual crank angle caused by a discrepancy between the actual point in time of the occurrence of reverse rotation and the point in time of the detection of the reverse rotation. The counter C is reduced by the subtraction value Y. As a result, reverse direction of the engine is readily detected without providing a dedicated sensor, and the counter is reliably caused to correspond to the actual crank angle.