To easily assemble a frame, and reuse a joining body by arranging the joining body fittable between mutually contacting end parts of a frame member in a wall panel structure for sticking a reverse frame of a decorative plate.

In a contact plane, an upper frame member 14a is butted against an end part side surface of a longitudinal frame member 12a to be fitted to and installed on an L-shaped and corner part right-angled joining body 15 to be joined at a right angle. Resilient locking pieces 152 are erected from both side ends of a bottom plate 151, and a width between the tips of these locking pieces 152, 152 is formed slightly smaller than a width of the longitudinal frame member 12a. With such constitution, the longitudinal frame member 12a can be easily held by resiliency of the locking pieces 152, 152. Thus, a frame can be assembled in a short time, there is no need to preassemble the frame, and since a wall panel structure can be stored in a state of a frame member, an assembling cost and a storage cost can be reduced.