An internal combustion engine can use ammonia and a non-ammonia fuel which is easier to burn than ammonia as fuel. The non-ammonia fuel is directly injected into a combustion chamber by a non-ammonia fuel injector, and the injected non-ammonia fuel is ignited, whereby combustion of the air-fuel mixture in the combustion chamber is commenced. In the control system of the internal combustion engine, the injection timing of the non-ammonia fuel is advanced at a time when a ratio of ammonia in all fuel fed to the internal combustion engine is high in comparison with the time when the ratio is low. Therefore, a control system of an internal combustion engine capable of using ammonia and a non-ammonia fuel (gasoline, light oil, hydrogen, etc.) which is easier to burn than ammonia, which suitably feeds fuel and controls combustion in order to suitably burn an air-fuel mixture in a combustion chamber is provided.