To realize a lightweight fireproof structure with a fire resistance capacity of 30 min or more, a wall area index of 1.0 or more, and a one-side thickness of 25-35 mm or less.

Various types of honeycomb-structure paper materials, an aluminum plate, a synthetic resin plate, wooden plywood and the like impregnated with or coated with a fireproof agent mainly composed of soluble silicates, and various types of heat insulating materials such as glass wool and rock wool if necessary, are integrated with a noncombustible board having a glass fiber as a facing material, composed mainly of magnesium carbonate and having a thickness of 2.4 mm or more into a unit structure. A sandwich structure is formed by inserting the various insulating substrates to dispose the noncombustible boards with the thickness of 2.4 mm or more on both sides. The structure with the fire resistance efficiency of ≥30 min and ≤3 hours is realized. Because the strength of the various insulating substrates is added, a wall are index, which is a disadvantage of a conventional structure mainly composed of an inorganic board heretofore, of not less than 1.0 is attained so that the lightweight structure can be designed. The fire resistance efficiency of ≥1 hour and ≤3 hours can be realized by designing the thickness of the noncombustible board and the selection/combination of the insulating substrates.