PURPOSE: To control the concentration of ozone in exhaust gas at a certain value or lower by providing a nozzle to spray a liquid for decomposing ozone near an outlet of an ozone deodorization passage having a suction section in a toilet stool to decompose residual ozone.
CONSTITUTION: A spray nozzle 27 is provided near an outlet 13 of an ozone deodorization passage G, having a suction section 12 in a toilet stool, of an ozone deodorizer C installed in the stool. And a tank 27a is provided to store alkaline liquid for decomposition of ozone, whereby the liquid is supplied to the nozzle 27 by means of a pump 27b. After being deodorized, the excessive ozone in exhaust gas in dissolved into a decomposition liquid to decompose the ozone, reducing thereby the amount of ozone in the exhaust gas. As a result, ozone concentration in exhaust gas can be controlled.