PURPOSE: To easily and safely replace a filter for decomposing ozone by moving a movable holder for an ozonizer while interlocking the pulling-out actuation of a reaction vessel and providing a safety switch which regulates electrification for the ozonizer according to movement of this movable holder and permits electrification according to return of the movable holder.

CONSTITUTION: When a reaction vessel 4 is pulled out from a casing 1, a movable holder 8 is rotated to the reaction vessel 4 counterclockwise. Thereby an elastic contact 92 is separated from the terminal 91 of a safety switch 9 and electrification for an ozonizer 3 is interrupted. Therefor, even when interruption of electrification for the ozonizer 3 is forgotten in the case of replacing the reaction vessel 4, it is prevented that large amounts of ozone may be discharged into the chamber. Further, when the reaction vessel is introduced into the casing 1, the movable holder 8 is rotated to the introduction actuation of the reaction vessel 4 clockwise. The elastic contact 92 is again brought into contact with the terminal 91 and thereby electrification for the ozonizer 3 can be permitted.