To provide a mounting structure of a surface panel in a wall member quickly, easily, and hermetically fitted thereto without rattling.

This assembling structure is provided with a wall body 7, which is constituted of a support member 8 comprising the inside and a surface panel 6 comprising the front side, and paired detachable lock parts 9 positioned between the support member 8 and the surface panel 6 and vertically sliding the surface panel 6 to the support member 8 to detachably lock it. At least, one of the detachable lock parts 9 is formed into a hook cross section in the side view so that, when one detachable lock part 9 is inserted downward and locked to the other detachable lock part 9, the front panel 6 is fixed and regulated in a hermetic state in the detachable lock part 9 and prevented from moving downward or in the separating direction from the support member 8.