In an internal combustion engine, an exhaust purification catalyst and a hydrocarbon feed valve are arranged in an exhaust passage. When the air-fuel ratio of the exhaust gas which flows into the exhaust purification catalyst should be made rich, rich control, which makes the air-fuel ratio of the exhaust gas which is exhausted from the combustion chamber rich, is performed. In order to prevent clogging of the hydrocarbon feed valve, clogging preventing injection which injects hydrocarbons from the hydrocarbon feed valve by an injection interval ΔtCB is performed. The exhaust purification catalyst has an oxygen storage ability. At the initial period of rich control, clogging preventing injection is performed by a shorter injection interval ΔtCS.