PURPOSE:To select the action or halt of a valve, by providing a sliding member in a stopper between a cam and a valve stem end so that the member follows the cam and slides in the longitudinal direction of a valve stem, and by engaging or disengaging the sliding member with or from the stopper. CONSTITUTION:A stopper body 1, which is placed in contact with the end 12a of a valve stem, is provided in the guide hole 19a of a cylinder head 19 so that the stopper body can be moved back and forth. A slider 2, which follows a rocker arm 9 and can slide in the longitudinal direction of the valve stem, is provided in the stopper body 1. A stopper pin 4, which is operated by a stopper cam 6, is provided in the stopper body 1. When the stopper pin 4 is pushed in, it comes into contact with the lower end of the slider 2 so that the motion of the rocker arm 9 is directly transmitted to a valve. When the pin 4 is moved out, the motion of the valve is stopped.