A seatbelt retractor mounted at a seatback of a reclining type seat provided in a vehicle, the seatbelt retractor comprising: a spindle which winds up a seatbelt; an acceleration sensor which detects acceleration in a vehicle front-back direction; and a locking mechanism which locks drawing-out operation of the seatbelt in response to acceleration detected by the acceleration sensor, wherein the acceleration sensor comprises a sensor cover which tilts together with the seatback, a sensor housing having an inertial body-support surface and supported swingably with respect to the sensor cover around an axial line in a vehicle-width direction to swing in the vehicle front-back direction with respect to the sensor cover when the seatback is tilted, an inertial body supported on the inertial body-support surface and displaced from a neutral position when the acceleration reaches at least a prescribed value, and an actuating member which operates synchronously with movement of the inertial body in the vehicle front-back direction and actuates the locking mechanism to a locking side, the sensor housing comprises an external teeth part having a plurality of teeth arranged in a circular-arc shape, the retractor further comprising a lever member coupled to the shaft of the spindle by a friction coupling, wherein the lever member turns in a first direction in which an engagement part provided at a tip end thereof is engaged with the external teeth part when the spindle rotates in a seatbelt drawing-out direction and turns in a second direction in which the engagement part moves apart from the external teeth part when the spindle rotates in a seatbelt winding-up direction, characterized in that a gap part not having the teeth is formed at a part of the external teeth part. a spindle which winds up a seatbelt; an acceleration sensor which detects acceleration in a vehicle front-back direction; and a locking mechanism which locks drawing-out operation of the seatbelt in response to acceleration detected by the acceleration sensor, wherein the acceleration sensor comprises a sensor cover which tilts together with the seatback, a sensor housing having an inertial body-support surface and supported swingably with respect to the sensor cover around an axial line in a vehicle-width direction to swing in the vehicle front-back direction with respect to the sensor cover when the seatback is tilted, an inertial body supported on the inertial body-support surface and displaced from a neutral position when the acceleration reaches at least a prescribed value, and an actuating member which operates synchronously with movement of the inertial body in the vehicle front-back direction and actuates the locking mechanism to a locking side, the sensor housing comprises an external teeth part having a plurality of teeth arranged in a circular-arc shape, the retractor further comprising a lever member coupled to the shaft of the spindle by a friction coupling, wherein the lever member turns in a first direction in which an engagement part provided at a tip end thereof is engaged with the external teeth part when the spindle rotates in a seatbelt drawing-out direction and turns in a second direction in which the engagement part moves apart from the external teeth part when the spindle rotates in a seatbelt winding-up direction, characterized in that a gap part not having the teeth is formed at a part of the external teeth part.