PURPOSE: To mount a fixture for a cavity wall at any place at any time without executing a foundation reinforcing material in a wall.

CONSTITUTION: A hole slightly larger than the breadth of a holding plate 1 is bored to a wallboard 1 by a drill, etc., the holding plate 1 is inserted into a wall from the indoor side, and the holding plate 1 is fast stuck onto the wallboard 13. A connecting part 5 is inserted to the wallboard 13. A guide wire 2 is bent to the wallboard 13 side, and cut at the place of the cutting section of the guide wire and fixed temporarily. A towel rail, etc., 7 are applied, a screw 9 is passed through the tapped hole 6 of the connecting part 5, and the towel rail, etc., and the holding plate 1 are clamped by the screw section 3 of the holding plate 1 and the screw 9.