To prevent a face plate of a wall panel from being cracked or fractured prior to happening after the construction of an attachment by a simple structure at low cost.

This fitting structure of an attachment to a wall panel is so constituted that a counter 4a as an attachment 4 is fitted in such a state as projected from the surface of the wall panel 1 having a face plate 2 attached to the front face 3 of a frame 3. A reinforcing plate 5 is fixed to a rear face 2b opposed to the surface 2a part of the face plate 2 to which the counter 4a is attached. A patch member 6 fixed to the rear face 5a of the reinforcing plate 5 is brought in contact with the rear face 3a of the frame 3.