An engagement and disengagement device used in a seat belt retractor including a first rotating member capable of being driven to rotate about a rotation axis thereof, a second rotating member provided coaxially with the first rotating member and connected to a reel of the seat belt retractor in an anti-torsion manner, and a transmission member provided between the first and second rotating member. The first rotating member is capable of transmitting torque to the second rotating member by means of the transmission member. The transmission member includes a holder and a transmission element in the holder. A first elastic component elastically holds the transmission element by radially exerting a force that enables the transmission element to be located away from the first or the second rotating member, and the first elastic component is integrated on the holder.