A seat belt retractor including a compact brake system configured so that when a drive member of the brake system is inoperative, an operation control member is held in an inoperative position. In this state, rotation stop portions of the operation control member are held in positions opposed to the flat surfaces of an energy-absorbing-member support member, and the energy-absorbing-member support member is braked by the operation control member, whereby the rotation is stopped. When the drive member is activated, the operation control member is moved downward, so that the rotation allowable portion of the operation control member is located on the cylinder of the energy-absorbing-member support member. Then the brake applied to the energy-absorbing-member support member can be released to allow the rotation of the energy-absorbing-member support member.