An internal combustion engine in which a main SOx trap catalyst able to trap SOx contained in exhaust gas is arranged in an engine exhaust passage, and the exhaust passage downstream of the main SOx trap catalyst is divided into a main exhaust passage and a bypass passage bypassing the main exhaust passage. An NOx storage catalyst is arranged in the main exhaust passage, and an auxiliary SOx trap catalyst is arranged in the main exhaust passage upstream of the NOx storage catalyst. Normally, the exhaust gas is made to flow in the main exhaust passage. When regenerating the main SOx trap catalyst, the exhaust gas is made to flow through the bypass passage.