PURPOSE: To prevent the fall of the simple substance sulfur and sulfide sticking to the vapor phase part of a reaction chamber into the liquid phase part in the reaction chamber and to make always good treatment by providing a trough for receiving the sulfide along the inside wall surface of the reaction chamber in the vapor phase part of the upper part of the reaction chamber.

CONSTITUTION: The hydrogen sulfide in a generated fermentation gas changes to the simple substance sulfur or sulfide which sticks to the front surface 3a of the reaction chamber. The deposits contain the moisture evaporating from the reaction chamber 3 and, therefore, glide along the front surface 3a of the reaction chamber. The deposits are received by the sulfide receiving trough 8. The simple substance sulfur or sulfide accumulating in the sulfide receiving trough 8 is periodically flushed out of a washing water discharge pipeline 11 by opening valves 10 and 12 and supplying the washing water, such as industrial water or city water from a washing water supplying pipeline 9. The simple substance sulfur or sulfide sticking on the front surface 3a of the reaction chamber glides along the wall surface and, therefore, the front surface is preferably made into a conical structure having about 45° angle of inclination.