Exhaust gas purifying of lean-burn internal combustion engine

An exhaust gas purifying apparatus of a lean-burn internal combustion engine, comprising:

• a lean-burn internal combustion engine capable of burning an air-fuel mixture in an oxygen excessive state;
• gas supply means for supplying an intake system of said lean-burn internal combustion engine with a vapor fuel gas containing a vapor fuel generated in a fuel tank;
• a nitrogen oxide occluding/reducing catalyst, provided in an exhaust system of said lean-burn internal combustion engine, for occluding nitrogen oxide in the exhaust gas when the exhaust gas is in the oxygen excessive state, and purifying the occluded nitrogen oxide when an oxygen concentration in the exhaust gas decreases;
• gas state judging means for judging a state of the vapor fuel gas supplied to the intake system of said lean-burn internal combustion engine;
• and
• exhaust state control means for setting, to a desired state, an air/fuel ratio of the exhaust gas flowing to said nitrogen oxide occluding/reducing catalyst by selectively controlling a fuel injection valve of said lean-burn internal combustion engine and said gas supply means in accordance with the state of the vapor fuel gas which is judged by said gas state judging means at a timing when the nitrogen oxide occluded by said nitrogen oxide occluding/reducing catalyst should be purified.