PURPOSE: To make the reset of valve system to full cylinder operation from cylinder cut off operation or the change of valve timing smooth by providing an energizing means for pressing the tip of a second rocker arm to the stem head of a valve.

CONSTITUTION: A valve system for an engine is provided with a spring 21 serving as an energizing means interposed between the tip 3b side of a second rocker arm 3 and a part unrelated to the movement of the valve system so as to press the tip 3b of the second rocker arm 3 to the stem head 9a of a valve 9. This spring 21 is so constituted that energizing force acts only before the lift of the valve 9 and in the initial stage of lift from before the lift and that the energizing force is gradually reduced in association with the lift of the valve 9. Springing-up at the cylinder cut off time and the jump of the valve during the lift are thereby prevented, so that the reset of the valve mechanism to full cylinder operation from cylinder cut off operation or the change of valve timing can be performed smoothly.