EXHAUST GAS PURIFICATION SYSTEM

It effectively suppresses that a catalyst temperature at the time of an SOx purge is excessively raised or lowered. The exhaust purification system includes: an NOx reduction type catalyst 32 which is provided in an exhaust system of an internal combustion engine and reduces and purifies NOx in an exhaust gas; a temperature sensor 44 which acquires a catalyst temperature of the NOx reduction type catalyst 32; and a regeneration treatment unit 50 which executes a catalyst regeneration to recover an NOx purification capacity of the NOx reduction type catalyst 32, in which the regeneration treatment unit 50 alternately executes a rich control which sets an exhaust air fuel ratio to a rich state so as to raise a temperature of the NOx reduction type catalyst 32 to a predetermined target temperature and a lean control which sets the exhaust air fuel ratio to a lean state so as to lower the temperature of the NOx reduction type catalyst 32, and sets an execution period of the lean control by a PID control from a deviation between the catalyst temperature acquired by the temperature sensor 44 during the previous rich control and the target temperature.