Exhaust gas purification device of an engine

An exhaust gas purification device of an engine having an exhaust passage, said device comprising:

• a NO.sub.x absorbent arranged in the exhaust passage and absorbing NO.sub.x when an air-fuel ratio of exhaust gas flowing into said NO.sub.x absorbent is lean, said NO.sub.x absorbent releasing absorbed NO.sub.x when the concentration of oxygen in the exhaust gas flowing into said NO.sub.x absorbent is lowered;
• determining means for determining whether an engine operating region belongs to a first engine operating region in which an air-fuel ratio of an air-fuel mixture fed into the engine should be made approximately the stoichiometric air-fuel ratio or a second engine operating region in which the amount of fuel fed into the engine is reduced below the amount of fuel which is necessary to make said air-fuel ratio of the air-fuel mixture the stoichiometric air-fuel ratio;
• and
• an air-fuel ratio control means for controlling said air-fuel ratio of the air-fuel mixture to make said air-fuel ratio of the air-fuel mixture approximately the stoichiometric air-fuel ratio after temporarily making said air-fuel ratio of the air-fuel mixture rich when the engine operating region is changed over from said second engine operating region to said first engine operating region.