A valve driving device (10), that converts rotational motion outputted from a valve-driving source to linear motion through cam mechanisms (13) provided to respective cylinders (2) and drives valves (3) in respective cylinders through the linear motion, the valve driving device is equipped with electric motors (11, 12) that are shared as the valve-driving source in a group of cylinders comprising a plurality of cylinders in which open-valve periods of the valves do not overlap; and motion-transmission mechanisms (14, 15) that transmit rotational motion of the electric motors (11, 12) to cams (16) in respective cam mechanisms (13) in the group of cylinders.