To easily constitute a storage chamber for maintaining an atmosphere of constant temperature and constant humidity.

A portal member whose cross section is an inverted U shape is mounted on a leveled ground surface, wall members are erected, the wall members are provided side by side in multiple lines, and a ceiling member is disposed. An upper part of the adjacent wall member is covered with a ceiling, a back side of the adjacent wall member is blocked by a back wall member, a floor surface is leveled and finished, and a space whose entrance side is sealed with a front wall member and an opening/closing door to constitute the storage chamber. A heat insulating moisture retention member is filled in a space part of the portal member, and the entire storage chamber is covered with the heat insulating moisture retention member. Thus, the storage chamber is configured by tactfully utilizing the portal member whose cross section is the inverted U shape, and the storage chamber is easily and strongly constructed at a low cost.