A seat belt retractor is provided that realizes the proper meshing between a plurality of internal teeth and external teeth with a simple movement of a spool. In the case of an emergency, external teeth of a pawl provided at a spool right side end mesh with internal teeth provided on a frame, and, with load acting on a seat belt, a spool left side end contacts a spool guide. Since the spool left side end tends to move further in the direction of seat belt load, the spool guide brings one external tooth at the spool left side end into contact with one target internal tooth provided on the frame. Hence, some of the spool external teeth are made to mesh properly with the respective internal teeth. Thus, some of the spool external teeth effectively mesh with the respective frame internal teeth with simple movement of the spool.