To appropriately reinforce a back plate without damaging the function and to prevent the deformation and damage of a satchel or the like in the satchel or the like provided with the adjustment mechanism of a shoulder belt.

This reinforcing structure A of the back plate of the satchel or the like is composed of the back plate 1, the adjustment mechanism 2 arranged on the front side, the flexible reinforcing plate 3 of the practically same width as the back plate 1 and a vertical length shorter than the back plate 1 arranged so as to make an upper end part be along the upper end of the back plate on the inner surface side of the back plate 1, and plural pins 4 for integrating the adjustment mechanism 2, the back plate 1 and the reinforcing plate 3.