An ammonia burning internal combustion engine can feed ammonia and a highly combustible substance burning easier than ammonia to a combustion chamber. When the amount of ammonia fed into the combustion chamber is increased or when the ratio of the amount of the ammonia to the total amount of the ammonia and the highly combustible substance fed into the combustion chamber is increased, the operating parameters of the internal combustion engine are controlled so the air-fuel mixture fed into the combustion chamber is made easier to burn. As a result, an ammonia burning internal combustion engine designed to suppress a drop in combustibility of auxiliary fuel due to ammonia, can be provided.