In an internal combustion engine, inside of an engine exhaust passage, a hydrocarbon feed valve and an exhaust purification catalyst are arranged. On the exhaust purification catalyst, platinum Pt is carried and a basic layer is formed. The concentration of hydrocarbons which flows into the exhaust purification catalyst is made to vibrate by within a predetermined range of amplitude and a predetermined range of period due to which the NOx which is contained in exhaust gas is reduced at the exhaust purification catalyst. At this time, the greater the oxidizing strength of the exhaust purification catalyst, the greater the injection pressure of hydrocarbons from the hydrocarbon feed valve.