To provide a seat belt retractor and a seat belt device capable of shortening time taken to restrict rotation of a spool. A seat belt retractor according to the present invention includes a spool 2, a base frame 3, a spring unit 4, a vehicle sensor 5, a locking mechanism 6, and a pretensioner 7. The locking mechanism 6 includes a lock gear 61 and a retainer 62. The lock gear 61 includes an outer circumferential wall 61a that is disposed at an end portion of the spool 2 and engageable with the vehicle sensor 5. The retainer 62 includes an inner circumferential wall 62a disposed on the inner side of the outer circumferential wall 61a and a side wall 62e that defines a space accommodating the lock gear 61. The lock gear 61 becomes engaged with the inner circumferential wall 62a or the side wall 62e of the retainer 62 when the lock gear 61 becomes eccentric relative to the retainer 62.