A variable valve mechanism is installed to change the operating angle and lift amount of an intake valve in accordance with the rotation position of a control shaft. A worm wheel is secured to the control shaft. The worm wheel is coupled to a motor actuator via a worm gear. The motor actuator is controlled during a normal operation so that the rotation position of the control shaft changes within a normal rotation range. A low-end stopper and high-end stopper are installed outside the normal rotation range to mechanically restrict the rotation of the control shaft.