To provide a wall panel mounting structure which contributes to forming an external wall substrate that is finished without joints, in a manner eliminating risks of cracking and breakage of an external wall in spite of jolts of a skeleton of a building.

The wall panel mounting structure is implemented by a wall panel mounting fitting which is integrally formed of base portions 2 including two vertical planes abutting on the skeleton of the building, a support portion tying upper ends of the two planes of the base portions 2 together, bent portions horizontally extending from lower edges of the respective base portions 2 along a header of a wall panel, and rise portions 5-a, 5-b vertically rising upward from the tips of the respective bent portions. The wall panel mounting fitting has an inverted L-shaped cross section. The support portion has formed therein a screw hole 6 formed therein, for penetrating therein a nail or a screw to be driven into the skeleton, and each bent portion has a claw 4 protruded therefrom, for engaging in the header of the wall panel to secure the fitting to the wall panel. A fitting which has a bent portion different from that of the above-mentioned fitting or a claw bent at an angle different from that of the above fitting may be applicable depending on the location where the fitting is secured.