Disclosed is an exhaust gas purifying apparatus which can efficiently decrease nitrogen oxides contained in an exhaust gas. The exhaust gas purifying apparatus is provided with: an exhaust pipe for guiding an exhaust gas discharged from an internal combustion engine; a catalyst means which is arranged in the downstream of the internal combustion engine in the exhaust gas flow direction and comprises a nitrogen oxide absorbing/reducing catalyst that absorbs nitrogen oxides contained in the exhaust gas, and a supporting mechanism that is arranged within the exhaust pipe and supports the nitrogen oxide absorbing/reducing catalyst within the exhaust pipe; a reducing agent spray means for spraying a reducing agent onto the catalyst means within the exhaust pipe; a concentration measuring meanswhich is arranged in the downstream of the catalyst means in the exhaust gas flow direction and measures the nitrogen oxide concentration in the exhaust gas that has passed through the nitrogen oxideabsorbing/reducing catalyst; and a control means for controlling whether the reducing agent should be sprayed from the reducing agent spray means or not according to the nitrogen oxide concentration measured by the concentration measuring means.