An exhaust gas purification system comprising: a diesel particulate defuser being configured to collect particulate matter contained in exhaust gas and being connected to an exhaust pipe of a diesel engine, an exhaust pipe injector being configured to perform exhaust gas injection; an exhaust gas temperature sensor (30a, 30b) being configured to detect an exhaust gas temperature of the diesel engine, an engine control unit, wherein the engine control unit is configured to increase the exhaust gas temperature by causing the exhaust pipe injector to perform the exhaust pipe injection and to automatically regenerate the diesel particulate defuser when an amount of particulate matter in the diesel particulate defuser becomes equal to or greater than a predetermined amount, an exhaust gas temperature sensor (30a, 30b) being configured to detect the exhaust gas temperature during automatic regeneration, wherein the engine control unit is configured to determine a difference between the detected exhaust gas temperature and a target regeneration temperature and to PID control an exhaust pipe injection amount based on the difference, and an exhaust brake valve, characterized in that, in a case where the exhaust pipe injection amount is PID controlled based on the difference, the engine control unit is configured, when the exhaust brake valve is closed during traveling automatic regeneration, to stop the exhaust pipe injection and to continue calculation of an integral control term by the PID control as long as the exhaust valve brake valve is closed, and, when the exhaust brake valve is opened, to take the integral control term that has been continuously calculated as an initial operation amount. a diesel particulate defuser being configured to collect particulate matter contained in exhaust gas and being connected to an exhaust pipe of a diesel engine, an exhaust pipe injector being configured to perform exhaust gas injection; an exhaust gas temperature sensor (30a, 30b) being configured to detect an exhaust gas temperature of the diesel engine, an engine control unit, wherein the engine control unit is configured to increase the exhaust gas temperature by causing the exhaust pipe injector to perform the exhaust pipe injection and to automatically regenerate the diesel particulate defuser when an amount of particulate matter in the diesel particulate defuser becomes equal to or greater than a predetermined amount, an exhaust gas temperature sensor (30a, 30b) being configured to detect the exhaust gas temperature during automatic regeneration, wherein the engine control unit is configured to determine a difference between the detected exhaust gas temperature and a target regeneration temperature and to PID control an exhaust pipe injection amount based on the difference, and an exhaust brake valve, characterized in that, in a case where the exhaust pipe injection amount is PID controlled based on the difference, the engine control unit is configured, when the exhaust brake valve is closed during traveling automatic regeneration, to stop the exhaust pipe injection and to continue calculation of an integral control term by the PID control as long as the exhaust valve brake valve is closed, and, when the exhaust brake valve is opened, to take the integral control term that has been continuously calculated as an initial operation amount.