To provide a structure of attaching an insert nut to a panel material capable of improving both tensile strength and shear strength of the insert nut while suppressing increase in weight and cost.

The insert nut 18 is provided in the panel member 30, which is composed of a core member 12 having a honeycomb structure and first and second surface plates 14 and 16 comprising fiber-reinforced plastic. A reinforcing member 22 is disposed at the part of the core member 12 where the insert nut 18 is provided. The insert nut 18 is housed in a hole 1402 of the first surface plate 14, a hole 3202 of a first metal plate 32, and a hole 2202 of the reinforcing member 22 and is attached by an adhesive agent 20. An inner peripheral surface 3202A of the hole 3202 of the first metal plate 32 and an outer peripheral surface 1804A of the insert nut 18 are in contact with each other.