A switching mechanism (100) in a force limiter mechanism of a seat belt retractor including: a locking mechanism including a locking element (68) that locks a torque tube (64) with respect to a spindle (61) so that the torque tube (64) rotates together with the spindle (61) and a spindle ring (70); a switch ring (120) rotatable to unlock the locking mechanism; and a switch housing (101) that stores the switch ring (120), a switch piston (115) adapted to activate the switch ring (120). A switching gas generator (116) generates gas for pushing out the switch piston (115) upon activation of the switching mechanism. The switch housing (101) of the switching mechanism (100) has a protrusion (110) that protrudes in an incoming direction of an operated part (122) at an abutment part hit by the switch ring (120) rotated by the switch piston (115) to control movement of the switch ring.