A seat belt buckle is disclosed in which play between a buckle base and a buckle button caused by vibration during the operation of an automobile is prevented, so that the tips of a pair of arm leaves formed on the buckle button are elastically pressed against the outer surfaces of a pair of upright plates on the buckle base to prevent lateral play between the buckle base and the buckle button, while vertical play is prevented by the elastic pressure from the tips of another pair of arm leaves against the upright plates.
