A seat belt retractor for retracting a seat belt includes a spool for retracting the seat belt, a locking mechanism for locking rotation of said spool, and an end-lock preventing mechanism for preventing an end-lock of the seat belt. The end-lock preventing mechanism includes a first speed-reduction portion for largely reducing a seat belt retracting speed of the spool when the spool retracts a substantially full length of the seat belt, and a second speed-reduction portion for reducing the seat belt retracting speed less than that of the first speed-reduction portion so as to provide a delay for the locking mechanism to be brought to a non-lock position at least when retraction of the seat belt is finished.