To secure a favorable contact state between a cam and a valve over a long period of time.

This valve driving device is provided with the cam 19 for driving the valve 11. The valve has a sliding contact member 16 providing a valve side sliding contact surface 31 brought into sliding contact with the cam. The cam has a cylindrical part 28 and a cam part 29. The projecting amount of the cam part from the cylindrical part changes along the axis of rotation. The cam is displaced to the sliding contact member in the direction of axis of rotation. The inclined surface of the valve side sliding contact surface can be fitted to the outer surface of the cam part and brought into sliding contact with it. When not into sliding contact, the parallel surface of the valve side sliding contact surface is fitted to the outer surface of the cylindrical part of the cam and brought into sliding contact with it.