Abstract: A seat belt retractor which achieves more stable performance of a pretensioner is provided. The seat belt retractor includes a spool for winding up a belt thereon. The spool has a shaft portion, a spool gear, and a spring-biased shaft projection which are disposed to project from a face of the spool. A spool bearing (or ring-like collar) is fitted around the shaft portion of the spool. The spool bearing is made of a material having high hardness and high rigidity such as SUS or SC. By this spool bearing, the spool is prevented from being directly subjected to load, like a bearing.