To automatically lock a baggage cage when a bag is placed therein, to fix the bag onto a mounting surface with no troublesome work required, and to make its fixed condition difficult to be seen from the outside.

This device comprises a hook unit 1 mounted in a bottom surface of a bag and a lock mechanism 11 mounted in a mounting surface mounting the bag to fix it to the mounting surface by locking the hook unit. The lock mechanism has a receiver 13, operating rod 14, and releasing members 19, 20. The receiver has a groove part 13a receiving the hook unit. The operating rod has a slope 16a in a tip end part of a rod main unit, also the rod is energized by a spring material to a lock position where the slope traverses in a groove of the receiver, ad the tip end part takes refuge from in the groove of te receiver against energizing force of the spring material when the hook unit abuts to the slope from upward to press it, on the other hand, the tip end part is reset to the lock position by energizing force of the spring material to lock the hook unit into the groove when the hook unit is fitted into the groove. The releasing member retreats the operating rod forcibly from the lock position to a retreat position.