To provide a storage space capable of storing things for a long period of time without giving anxiety to the owner by creating an optimum environment for storage by controlling as far as possible the transmission of underground temperature directly to the inside of the storage space thereby eliminating the stagnation of air inside storage space and preventing the occurrence of molds or dew condensation.

This steel underground storage space is made of wall, floor and ceiling structural bodies 1A, 1B and 1C each of which has a metal exterior plate 3 on the exterior side of plural core steel members, and the body 20 of the box-shaped storage space is constructed. An insulation material 10 is provided in a space 9 formed between metal exterior plates 3 and interior finish boards 6 fixed to the inner side of steel members 2 in each of structural bodies 1A, 1B, 1C; forced suction and exhaust fans 17 for pressing in air in the storage at two points on the diagonal line in the body 20 of the storage, and a large number of small holes 18 jetting air from the space 9 to the storage are formed in the interior board 6 of the wall structural body 1A.