PURPOSE: To save remarkably an expense required for an exhaust treatment by placing a function for treating a waste gas by using a shower by an ultrasonic humidifier and a city water, on an exhaust system.

CONSTITUTION: Boron trichloride is led into an etching chamber 1 through a gas pipeline 9, a semiconductor wafer 4 is brought to dry etching, and thereafter, it is exhausted by a mechanical booster pump 6 and a rotary pump 7, and led into a waste gas treating part 24 through an exhaust pipe 21. To the waste gas treating part 24, a fog-like water content is supplied through a humidifying pipeline 12 from an ultrasonic humidifier 11, and an unconverted gas reacts to the fog-like water content and becomes boric acid. Also, to a shower nozzle 13, a city water is supplied, and boric acid adhering to a mesh 17 and a solid matter 16 is washed off by a shower and drained from a drain pipeline 18. In this way, waste gas which has been brought to waste gas treatment is exhausted to a main exhaust duct from an exhaust damper 20.