Abstract: In a seat belt retractor according to the present invention, an arcuate fall preventing flange 4m is provided on an outer surface of a guide flange 4b of the reel shaft. The central axis a.sub.2 of the reel shaft 4 is eccentrically shifted from the central axis a.sub.1 of the through-hole 2d of the right-hand side wall 2a by an eccentric amount "b" and the reel shaft is faced to the through-hole 2d to coincide the peripheral edge of the profile consisting of the left-hand guide flange 4c and the fall preventing flange 4r with the through-hole 2d. In this state, the reel shaft is passed through the through-hole 2d. After that, the reel shaft is moved upward to align the central axis a.sub.2 of the reel shaft 4 with the central axis a.sub.1 of the through-hole 2d of the right-hand side wall 2a. Thereby, the reel shaft 4 is assembled in the predetermined position of the frame.

Abstract: In a seat belt retractor according to the present invention, lock actuating means is actuated to engage locking pins with the engagement portion of a frame when deceleration in excess of a predetermined value acts upon the vehicle and/or when the seat belt is pulled at an acceleration in excess of a predetermined value. Reliable engagement is achieved since the engagement portion of the frame is engaged by the locking pins, unlike the prior art which is adapted to mesh the teeth on a reel shaft with the teeth on a frame. Accordingly, the reel shaft is assuredly locked against turning in the seat belt pulling direction, as a result of which reliability is enhanced.