PURPOSE: To open and close valves in response to low speed operation and high speed operation by bringing a low speed cam into contact with a cam-contact part when an internal combustion engine rotates at a low speed, and bringing a high speed cam into contact with a cam-contact part when the engine rotates at a high speed, thereby oscillating a rocker arm, respectively.

CONSTITUTION: When an internal combustion engine starts, oil pressure does not act on a piston 35 of a cylinder part 34, and thus the piston 35 is pressed by a return spring 36. Therefor, the piston 35 is located on the high speed variable cam contact part 27 side, and the high variable cam contact part 27 is kept separate from a low speed cam-contact part 29. As a result, when a cam shaft 17 is rotated to press a high speed- and low speed cams 30, 31 on the respective cam contact parts 27, 29, these cam contact parts operate separately. At this time, a rocker arm 15 is oscillated by the amount of projection of the low speed cam 31 to open and close an intake valve 11 in response to low speed operation. On the other hand, when oil, pressure acts on the piston 35 at the time of high speed operation, the rocker arm 15 is oscillated by the high speed cam 30. Thus, the contact part of the rocker arm with the cam shaft is switched by oil pressure to change the amount of valve lift and the timing.