An exhaust gas purification system which can suppress a decrease in engine torque during a desulfurization process applied to a NOx storage reduction catalyst. The system includes a NOx storage reduction catalyst in an exhaust pipe of an engine, and a desulfurization process control unit that controls an amount of intake air introduced to the engine to enrich the exhaust gas, and performs a desulfurization process to the NOx storage reduction catalyst. The desulfurization process control unit is configured to gradually reduce an amount of intake air when the desulfurization process is commenced.