Disclosed is a retractor for a seat belt including a spool around which a webbing is wound, a frame rotatably coupled with the spool, a flywheel gear provided at a central portion thereof with a driving gear, having one-directional gear teeth formed along an outer circumferential surface thereof, and mounted on one end of the spool, a vehicle sensor locked with the one-directional gear teeth if the frame is inclined at a predetermined angle or more, a lever locked with the one-directional gear teeth if the webbing is withdrawn by a predetermined first length, and separated from the one-directional teeth if the webbing is introduced again so that the webbing is withdrawn by the second length, and an integrated plate including a driven gear, a first plate to adjust the lever according to a withdrawn length of the webbing, and a second plate integrated with the first plate.