In an engine, an exhaust purification catalyst (13) and a hydrocarbon feed valve (15) are arranged in an engine exhaust passage, and, a low pressure exhaust gas recirculation system (LPL) which makes exhaust gas downstream of the exhaust purification catalyst (13) recirculate is provided. If hydrocarbons are injected from the hydrocarbon feed valve (15), a carbon dioxide which is generated at the exhaust purification catalyst (13) is recirculated, and the air-fuel ratio of the exhaust gas which flows into the exhaust purification catalyst (13) temporarily drops. Hydrocarbons are injected from the hydrocarbon feed valve (15) in synchronization with this temporary drop in the air-fuel ratio.