PURPOSE: To enhance the deodorizing efficiency, to exclude the pH treatment of a waste liquid and to prevent the additional gas generation during deodorizing operation by absorbing a malodorous gas containing an aldehyde or the like by a mixed aqueous solution of a fulfite and a hydroxylamine salt.

CONSTITUTION: The bad odor gas 2 containing an aldehydes, hydrocarbons and amines generated by the wet type oxidation treatment system of excretion is introduced into a lower part of an absorption and washing tower 1 and contacted with a packing layer of which all surface is scattered with a washing liquid 6 from a nozzle 4 and a gas 5 from which the aldehydes and hydrocarbons are absorbed and removed is discharged. The washing liquid is recirculated by a pump 8a and sodium sulfite and hydroxylamine hydrochloride are replenished respectively while the pH is controlled to a neutral zone by operating pH meters 7a, 7b and washing tower is additionally provided to a post-stage and the gas 5 treated in the anti-stage is introduced therein to absorb and remove residual bad odor such as amines or the like.