At the time of reference position learning, an operation amount of an actuator is set such that intake valve phase changes to a position of most retarded angle in a region where the amount of change in intake valve phase relative to the actuator operation amount is small (S110). When the intake valve phase reaches the position of most retarded angle and the change in the intake valve phase stops (YES at S140), it is determined that the intake valve phase has reached the position of most retarded angle as the reference phase, and learning is completed. Further, in response to completion of learning, power supply to the electric motor as the actuator is stopped. Consequently, it becomes possible to reduce power consumption and to protect the apparatus at the reference position learning for ensuring accuracy in detecting valve opening/closing timing.