PURPOSE: To provide a key driving device for an automatic playing device by comparatively simple structure by providing each key with an electromagnet, a rotatable shaft and a claw for hooking the shaft.

CONSTITUTION: An XYZ coordinate system is set up, and when it is defined that the shaft 11 is the Z axis and an intersecting point between the shaft 11 and the key 13 is an origin 0, X and Y axes are set up so that the position of the electromagnet 12 becomes (X, Y, Z)=(0, R, 0) when R is defined as an optional positive constant. When the shaft 11 is rotated in the clockwise direction from the positive direction of the Z axis and current is allowed to flow into the electromagnet 12 so as to reject the claw 16, force is applied to the claw in the negative direction and the claw 16 is moved in the negative direction and comes into contact with the shaft 11. Thereby, the claw 16 is hooked in a recessed part of the shaft 11. Since the claw 16 is fixed on the key 13, the key 13 is rotated around the shaft 11 in the clockwise direction from the positive direction of the Z axis and then stopped at the time of coming into contact with a stopper 14.