To enable rapid microorganism sterilization and access right after the sterilization without the change of equipment by hermetically closing devices and equipment in a simple booth and supplying gaseous chlorine dioxide to sterilize these devices and equipment, then removing the residual gaseous chlorine dioxide by a removing device.

The devices and equipment are hermetically closed by the simple booth; for example, a bag-shaped object consisting of the materials formed by using films of nylon, etc., having a high gas barrier property on the inner side and superposing polyolefin films on the outer side thereof. The gaseous chlorine dioxide is introduced from a chlorine dioxide generator into this booth in such a manner that the concn. of the gas attains about 1 to 500ppm, by which the devices and equipment are sterilized for about 1 to 24 hours. The residual gaseous chlorine dioxide is introduced into a the gaseous chlorine dioxide removing device and is removed by an oxidative gas removing agent after the sterilization treatment. For example, a two- stages system, etc., of forming an absorbent liquid by movable aq. soln. gas cleaning and sweep system and using this system together with active carbon are usable. The rapid sterilization and the immediate access after the end of the sterilization are made possible by this constitution.