Exhaust purification device for internal combustion engine

An exhaust purification system for an internal combustion engine, in which an exhaust purification catalyst is arranged in an engine exhaust passage and a hydrocarbon feed valve is arranged upstream of the exhaust purification catalyst in the engine exhaust passage, wherein a precious metal catalyst is carried on an exhaust gas flow surface of the exhaust purification catalyst and basic exhaust gas flow surface parts are formed around the precious metal catalyst, wherein the exhaust purification catalyst has the property of reducing the NOX contained in exhaust gas if a concentration of hydrocarbons flowing into the exhaust purification catalyst is made to vibrate at an amplitude within a predetermined range of amplitude and with a period within a predetermined range of period and has the property of a storage amount of NOX contained in exhaust gas increasing if a vibration period of the hydrocarbon concentration is made longer than the predetermined range of period, and wherein a first NOX purification method configured to inject hydrocarbons from the hydrocarbon feed valve with a period within the predetermined range of period to thereby purify the NOX contained in the exhaust gas and a second NOX purification method configured to make an air-fuel ratio of exhaust gas flowing into the exhaust purification catalyst rich with a period longer than the predetermined range of period to thereby make the exhaust purification catalyst release the stored NOX to purify the NOX are selectively used, wherein a first catalyst state region and a second catalyst state region are defined in a region in which an exhaust purification catalyst state can fall, that the first NOX purification method is used when the exhaust purification catalyst state falls in the first catalyst state region and the second NOX purification method is used when the exhaust purification catalyst state falls in the second catalyst state region, that the first catalyst state region and the second catalyst state region are respectively divided into proximal regions close to the other catalyst state regions and distal regions far from the other catalyst state regions, and that, when the exhaust purification catalyst state falls in the proximal region of one catalyst state region, shift control configured to shift the region in which the exhaust purification catalyst state falls to the other catalyst state region is performed, to thereby switch the NOX purification method used from the first NOX purification method to the second NOX purification method or from the second NOX purification method to the first NOX purification method.