To provide a composite panel and a method for mounting the composite panel attaining accurate positioning when mounting the composite panel to attain mounting work of high labor-saving effect as well as securing sufficient mounting strength while maintaining fine surface appearance without fittings appearing on the surface of the composite panel.

The composite panel attached to a wall surface or a ceiling surface of a building includes a rear plate, a core material and a front plate. The rear plate is provided with an insertion hole bored to allow a screw head of a locking screw to penetrate, and locking holes bored continuously on both sides of the insertion hole to make a screw part slidable but to be narrower than the outer diameter of the screw head. The core material is provided with a storage hole bored to make the screw head slidable in a portion corresponding to the insertion hole and locking holes of the rear plate at least.