In the exhaust gas purification system, a diesel particulate defuser (“DPD”) for trapping particulate matter (“PM”) in exhaust gas is connected to an exhaust pipe of an engine to automatically regenerate the DPD by raising a temperature of the exhaust gas from the engine by carrying out post injection when an amount of PM in the DPD exceeds a predetermined amount. Further, the system includes detecting the temperature of the exhaust gas during DPD regeneration when the DPD is automatically regenerated, calculating a deviation between the detected temperature of the exhaust gas and a target temperature for the DPD regeneration, and controlling a quantity of the post injection by resetting an integral control term used in a PID control to zero when running mode automatic regeneration is shifted to idling mode automatic regeneration after a vehicle is stopped, when PID-controlling the quantity of the post injection based on the deviation.