PURPOSE: To provide a device which can respond to a rotational body inertia moment or angle acceleration twice as much as before without deteriorating durability, in respect to a driving part of an ignition device for an internal combustion engine.

CONSTITUTION: Power of a driving shaft 1 is transmitted to a driven shaft 4 through screw gears 2, 6. The screw gear 6 on the side of the driven shaft 4 is divided into a main gear 7 adhered to the driven shaft 4 and an auxiliary gear 8 fitted movably in a thrust direction, together with the driven shaft 4 in a rotatable manner. When the main gear 7 is in contact with the auxiliary gear 8, their teeth are dislocated from each other. A compression spring 10 and a sliding plate 9 which generates rotational sliding resistance are arranged between the auxiliary gear 8 and a housing end face 3a. The auxiliary gear 8 is pressed in the direction of a housing, that is, in the reducing direction of the teeth dislocation, by means of the screw gear 2 on the side of the driven shaft, and the screw gear 2 is meshed with the gears 7, 8 on the driven shaft side.