To provide a marine structure exhaust gas purifying method, capable of reducing NOx emission, even when the exhaust gas is low in temperature.

In the purifying method of the exhaust gas exhausted from a diesel engine for marine structure, in which an absorbent enabling absorption of the nitrogen oxide is arranged between the engine and the NOx removal catalyst, the nitrogen oxide in the exhaust gas is absorbed in the absorbent, when the exhaust gas which comes in contact with the catalyst is low in temperature, desorbed at high temperatures, and the nitrogen oxide originally contained in the exhaust gas and the nitrogen oxide which is desorbed from the absorbent are reduced, by selective catalyst reduction process.