In an internal combustion engine, inside of an engine exhaust passage, a hydrocarbon feed valve (15) and an exhaust purification catalyst (13) are arranged. At the time of engine operation, the amplitude of change of the concentration of hydrocarbons which flow into the exhaust purification catalyst (13) is made to become within a predetermined range of amplitude by control of at least one of the injection time and injection pressure of hydrocarbons from the hydrocarbon feed valve (15). In this case, when only the injection time of hydrocarbons is controlled, the injection time of hydrocarbons under the same engine operating state is made longer the higher the temperature of the exhaust purification catalyst (13).