PURPOSE: To change height of a shoulder belt of which upper end part is connected to a shoulder belt installation plate by fixing the shoulder belt installation plate integrally with an elevation plate in such a way that the elevation plate moves vertically to an installation base plate fixed to a back side surface of a bag main body.

CONSTITUTION: An elevation plate 13 is disposed in a center space of an installation base plate 10, and assembled to be freely vertically movable to the installation base plate 10 in such a way that a lock claw 17 can be engaged with/ detached from a desired locking recess 15 by deformation of an arm member 16. A shoulder belt installation plate 12 is fixed to a surface of the elevation plate 13, so the elevation plate 13 is shielded on the back side. A lock plate 14 is vertically movably assembled to the installation base plate 10 and the elevation plate 13. A stopper 22 provided on the lock plate 14 is disposed between the arm members 16 on both sides at the elevation plate 13, and a handle 19 at an upper end of the lock plate 14 is protruded upward from the installation base plate 10. A lock protrusion 21 provided on a leg member 20 of the lock plate 14 is set slidable to a side surface of the elevation plate 13.