PURPOSE: To absorb, decompose, sterilize and remove a noxious and odorous substance by enhancing gas-liquid contact efficiency without using a packing material, by subjecting a noxious and odorous substance-containing fluid and a treating body to contact reaction in a static mixer.

CONSTITUTION: For example, when exhaust gas containing a noxious and odorous substance such as NH3 or HCl is treated, said exhaust gas is supplied to the static mixer 17 provided in an exhaust gas treatment apparatus 26 through a contact reaction line 16. A treating solution corresponding to the noxious substance in exhaust gas is supplied through an atomizing apparatus 21 and a supply nozzle 22, and the exhaust gas and the fine mist like treating solution are mixed under stirring in the static mixer 17 while flowed into said mixer in parallel to advance contact reaction and the noxious substance in the exhaust gas is absorbed during treatment. Purified exhaust gas is exhausted from an exhaust line 23 through a gas-liquid separation apparatus 24.