An engagement and disengagement device used in a seat belt retractor includes a first rotating member and a second rotating member configured to be coaxial, and a transmission member disposed between the first and second rotating members. The first rotating member defines an engagement portion on a radial inner surface thereof, and the distance from the engagement portion to an axis of rotation gradually increases in a first direction of rotation. The transmission member can rotate between an engagement position and a non-engagement position relative to the first rotating member.