Abstract: An automatic locking retractor for a seat belt assembly, which comprises a housing having a shaft for webbing, a spring for urging the shaft in a predetermined direction to cause rewinding of the webbing, a rachet wheel integrally fixed to the shaft, a pawl for locking the rachet wheel in position, a diameter-sensing element capable of sensing the diameter of the webbing wound about the shaft, and a control member. The control member has a first leg on one end and a second leg on the other end and is fitted on the shaft to permit movement between a pair of stoppers and to permit frictional sliding when one of the stoppers is engaged and the shaft continues to rotate. The rachet wheel has teeth for engagement with the pawl and these teeth are arranged at an interval almost equal to the distance between the first and second leg of the control member.