PURPOSE: To provide a vault with high heat insulating performance by providing a wall structure consisting of two synthetic resin foamed body layers formed with a space inbetween and concrete layers formed on the respective surface sides thereof.

CONSTITUTION: A wall 1 and a ceiling 2 have the same structure, in which concrete layers B are laminated on the surfaces of two lateral synthetic resin foamed body layers A formed with a space α inbetween. When a field spray foaming type synthetic resin foamed body layer A is formed, an incombustible material such as hard urethane foam is used as the material, the synthetic resin foamed body layer A is formed by spraying after either one of the lateral concrete layers B is formed, and the other concrete layer B is then formed. Otherwise, the lateral concrete layers B are preliminarily formed by use of a form, the form is thereafter removed, and the material is sprayed and injected to the void generated thereby to form the synthetic resin foamed body layer A. Since the synthetic resin foamed body layers and the space are interposed between the concrete layers, excellent airtightness and heat insulating property can be provided.