To safely store the material easy to be affected by the air and perform the work by providing an inlet of helium gas and an outlet to replace the air with the helium gas from an upper part in a space as the helium gas flows in and discharge the air from a lower part in the closed space, and providing a treatment space of the helium gas atmosphere in the space.

A treatment chamber in which the treatment space is a structure comprises side walls in the periphery and a ceiling in a closed manner, the helium flowing in from an inlet 2 is stored in an upper part of the treatment chamber as a helium layer HE while the air is pressed downward to form an air layer A. When helium gas successively flows in, the helium layer HE is increased in thickness and the air forming the air layer A is discharged out of the treatment chamber from an outlet 1. Finally, the air layer A is completely replaced with the helium layer HE, and helium is filled in the treatment chamber. Thus, the working efficiency of the work in which a large volume of dust is generated or the work which is not suitable in performing under the presence of dust, can be improved.