EXHAUST PURIFICATION DEVICE FOR INTERNAL COMBUSTION ENGINE

A NOx storing and reducing catalyst is disposed in an engine exhaust gas passage in which the catalyst stores NOx contained in the inflow exhaust gas when an air-fuel ratio of inflow exhaust gas is lean and releases and reduces the stored NOx when the air-fuel ratio of the inflow exhaust gas is rich. A stored NOx amount of the NOx storing and reducing catalyst is calculated and an exhaust gas purification operation is controlled based on the stored NOx amount. When the air-fuel ratio of inflow exhaust gas is lean, a ratio of NOx components in the inflow exhaust gas is calculated. An increment of the stored NOx amount per unit time is calculated based on the ratio of NOx components.