PURPOSE: To provide a decelerating driver wherein the adjusting shaft of devices to be adjusted of various types from a one-turn adjustment type up to a multiturn adjustment type is turned and the shaft can be adjusted fine.

CONSTITUTION: A decelerating mechanism 3 which is provided with a planet-gear mechanism composed of a sun gear 31, a planet gear 32 and an internal gear 33 and which is provided with an idling clutch function when an excessive load is applied and a driver bit 4 which is connected to the decelerating mechanism 3 and which is constituted so as to be retreated to the shaft direction when a prescribed load is applied to the shaft direction are installed. In addition, a holder 1 which houses the decelerating mechanism 3 and the driver bit 4 and which holds the internal gear 33 constituting the decelerating mechanism 3 so as not to be turned and a rotation-preventing member 5 which is coupled to or abuts on the body or the like of a device 7 to be adjusted and which prevents the holder 1 from being turned with reference to the device to be adjusted are provided.