An engagement and disengagement device used in a seat belt retractor, comprising: a first rotating member which can be driven to rotate around an axis of rotation; a second rotating member, wherein the second rotating member and the first rotating member are configured to be coaxial, and the second rotating member is used to be connected to a reel of the seat belt retractor in an anti-torsion manner; and a transmission member disposed between the first rotating member and the second rotating member, wherein the first rotating member can transmit, in a first direction of rotation, torque to the second rotating member via the transmission member, wherein the first rotating member defines an engagement portion on a radial inner surface thereof, the distance from the engagement portion to the axis of rotation gradually increases in the first direction of rotation, and the engagement portion is used to engage with the transmission member; and wherein the transmission member can rotate between an engagement position and a non-engagement position relative to the first rotating member, wherein when the transmission member is at the engagement position, the transmission member engages with both the first rotating member and the second rotating member, such that the first rotating member, the second rotating member, and the transmission member can rotate together; when the transmission member is at the non-engagement position, the transmission member does not engage with the first rotating member and the second rotating member, such that the first rotating member and the second rotating member can freely rotate relative to each other; characterized in that the transmission member comprises a cage and a transmission element, and the transmission element is disposed in the cage, and can move radially in a space defined between the engagement portion of the first rotating member and a radial outer surface of the second rotating member, and in that the device further comprises a first elastic component connected to the cage so as to elastically retain the transmission element in a radial direction. a first rotating member which can be driven to rotate around an axis of rotation; a second rotating member, wherein the second rotating member and the first rotating member are configured to be coaxial, and the second rotating member is used to be connected to a reel of the seat belt retractor in an anti-torsion manner; and a transmission member disposed between the first rotating member and the second rotating member, wherein the first rotating member can transmit, in a first direction of rotation, torque to the second rotating member via the transmission member, wherein the first rotating member defines an engagement portion on a radial inner surface thereof, the distance from the engagement portion to the axis of rotation gradually increases in the first direction of rotation, and the engagement portion is used to engage with the transmission member; and wherein the transmission member can rotate between an engagement position and a non-engagement position relative to the first rotating member, wherein when the transmission member is at the engagement position, the transmission member engages with both the first rotating member and the second rotating member, such that the first rotating member, the second rotating member, and the transmission member can rotate together; when the transmission member is at the non-engagement position, the transmission member does not engage with the first rotating member and the second rotating member, such that the first rotating member and the second rotating member can freely rotate relative to each other; characterized in that the transmission member comprises a cage and a transmission element, and the transmission element is disposed in the cage, and can move radially in a space defined between the engagement portion of the first rotating member and a radial outer surface of the second rotating member, and in that the device further comprises a first elastic component connected to the cage so as to elastically retain the transmission element in a radial direction.