A seatbelt retractor configured to ease the tightness of a seatbelt felt by an occupant when the occupant wearing the seatbelt reclines a seatback. An acceleration sensor 70 includes a sensor cover 71 which tilts with a seatback, a sensor housing 72 supported swingably with respect to the sensor cover 71 and having an inertial body support surface 78 and an inertial body 73 which is displaced when the acceleration reaches at least a prescribed value. The sensor housing 72 includes an external teeth part 84 having a plurality of external teeth 81 and 82 and a gap part 83 without external teeth. A lever member 90 is coupled to the shaft 22 of the spindle 20 by a friction coupling, and the lever member turns in a first direction in which an engagement part 92 is engaged with the external teeth part 84 when the spindle 20 rotates in a seatbelt drawing-out direction and turns in a second direction in which the engagement part 92 moves apart from the external teeth part 84 when the spindle 20 rotates in a seatbelt winding-up direction.