EXHAUST GAS PURIFICATION SYSTEM OF INTERNAL COMBUSTION ENGINE AND EXHAUST GAS PURIFICATION METHOD OF INTERNAL COMBUSTION ENGINE

An exhaust gas after-treatment device 31 including an oxidation catalyst 31a and a DPF 31b in order from an upstream side is provided in an exhaust passage 15 of an internal combustion engine 10. A target value Et of an EGR rate E in EGR control is set to be a second EGR rate E2 higher than a first EGR rate E1 at the time of a normal operation of the internal combustion engine 10 and the EGR control is performed, in a case where a catalyst index temperature T that indexes a temperature of the oxidation catalyst 31a falls within a set temperature region Rab between a lower limit set temperature Ta and an upper limit set temperature Tb which are preliminarily set, and where an estimated PM deposition amount V of the DPF 31b is less than a preliminarily set regeneration start threshold value Vc, after an operation state of the internal combustion engine 10 transitions from a traveling operation state to an idling operation state. Thereby, in the idling operation state after travel of a vehicle, generation of NO 2 by the oxidation catalyst 31a included in the exhaust gas after-treatment device 31 of the exhaust passage 15 is decreased, and emission of NO 2 to the atmosphere is suppressed.