To enable a tongue to be more compact in size even when a seat-belt locking member is disposed and to achieve satisfactory mountability. A tongue (7) includes a resin mold portion (12) having seat belt lock guide holes (21) and (22). The resin mold portion (12) is provided with a seat belt lock (13) such that it is movable between an unlocking position where it does not lock a seat belt (4) and a locking position where it locks the seat belt (4) while being guided by the seat belt lock guide holes (21) and (22), and the seat belt lock (13) is set in the unlocking position under normal conditions and is set in the locking position in emergency. The seat belt lock (13) is continuously urged toward the unlocking position by a torsion spring (14). In emergency, the seat belt lock (13) is set in the locking position by a pressing force from the seat belt (4) against the urging force of the torsion spring (14).