A retractor for a seat belt includes a winding force reducing mechanism for reducing a webbing winding force when an occupant wears the seat belt. The retractor includes a base; a winding shaft supported rotatably on base for winding a webbing; a first winding spring for energizing the winding shaft in a webbing winding direction; a second winding spring disposed on the winding shaft in parallel to said first winding spring; and gear unit interposed between the winding shaft and the second winding spring for applying the energizing force of the second winding spring to the winding shaft in the same direction as the energizing force of the first winding spring and for tightening the second winding spring in an elastic energy storing direction by means of the energizing force of the first winding spring. The gear unit is structured such that, when the seat belt is in use, the elastic energy of the second winding spring stored therein can act in a manner to cancel the energizing force of the first winding spring so that a reduced energizing force in the webbing winding direction can be applied to the winding shaft.