An exhaust gas purification system of an internal combustion engine, comprising: an oxidation catalyst that is provided in an exhaust passage of the internal combustion engine and has an oxidizing function; a fuel supplying unit that supplies a fuel component to the oxidation catalyst via exhaust gas flowing into the oxidation catalyst; an exhaust gas purifying unit that is provided in the exhaust passage on a downstream side of the oxidation catalyst and is formed so as to include a filter which collects particulate matter in the exhaust gas, and a selective reduction-type NOx catalyst which selectively reduces NOx in the exhaust gas using ammonia as a reducing agent; a reducing agent supplying unit (7, 8) that supplies ammonia or an ammonia precursor to the exhaust gas purifying unit via exhaust gas flowing into the exhaust gas purifying unit; and a supply control unit for controlling the fuel supplying unit and the reducing agent supplying unit (7,8), characterized in that the supply control unit is configured to, when a prescribed condition under which a part of the fuel component supplied by the fuel supplying unit passes through to the downstream side of the oxidation catalyst is satisfied, control the fuel supplying unit and the reducing agent supplying unit (7, 8) in such a manner that an amount of ammonia or ammonia precursor which is larger than a non-passing time supply amount supplied by the reducing agent supplying unit (7, 8) reaches the exhaust gas purifying unit before the fuel component supplied by the fuel supplying unit reaches the exhaust gas purifying unit, the non-passing time supply amount being an amount of the ammonia or ammonia precursor to be supplied by the reducing agent supplying unit (7,8) when the prescribed condition is not satisfied. an oxidation catalyst that is provided in an exhaust passage of the internal combustion engine and has an oxidizing function; a fuel supplying unit that supplies a fuel component to the oxidation catalyst via exhaust gas flowing into the oxidation catalyst; an exhaust gas purifying unit that is provided in the exhaust passage on a downstream side of the oxidation catalyst and is formed so as to include a filter which collects particulate matter in the exhaust gas, and a selective reduction-type NOx catalyst which selectively reduces NOx in the exhaust gas using ammonia as a reducing agent; a reducing agent supplying unit (7, 8) that supplies ammonia or an ammonia precursor to the exhaust gas purifying unit via exhaust gas flowing into the exhaust gas purifying unit; and a supply control unit for controlling the fuel supplying unit and the reducing agent supplying unit (7,8), characterized in that the supply control unit is configured to, when a prescribed condition under which a part of the fuel component supplied by the fuel supplying unit passes through to the downstream side of the oxidation catalyst is satisfied, control the fuel supplying unit and the reducing agent supplying unit (7, 8) in such a manner that an amount of ammonia or ammonia precursor which is larger than a non-passing time supply amount supplied by the reducing agent supplying unit (7, 8) reaches the exhaust gas purifying unit before the fuel component supplied by the fuel supplying unit reaches the exhaust gas purifying unit, the non-passing time supply amount being an amount of the ammonia or ammonia precursor to be supplied by the reducing agent supplying unit (7,8) when the prescribed condition is not satisfied.