To provide an outside insulation building with reinforced-concrete wall structure at an amazing low cost.

In an opening made between concrete bearing walls furnished with outside insulation composite panels P, when working on concrete forms for floor slabs, a mounting clamp 3 provided with an anchor portion 3b and a horizontal portion 3a is placed at a front-end part of a floor-slab form S so as not to be covered by floor-slab concrete. By placing floor concrete, the mounting clamp 3 is securely integrated with the floor slab S. Then mounting pores H, H1 in an upper frame 5a and/or lower frame 5b of the outside insulation composite panels P and a coupling pore H2 in a front part of a mounting plate 4 are fixed together by inserting a coupling pin 6 through them. The end part of the mounting plate 4 being adjusted to be correctly placed on the horizontal portion 3a and thus the mounting plate 4 being secured on the mounting clamp 3 via fixing pores, a curtain wall of only outside insulation composite panels P is formed in the opening between the concrete bearing walls.