A combustor includes a combustion tube having a cylindrical shape with a combustion space where fuel is combusted and including an inlet through which the fuel is introduced, an outlet through which a gas generated when the fuel is combusted is discharged, and a protrusion protruding inward from a wall surface between the inlet and the outlet; an injection unit configured to inject fuel into the combustion tube through the inlet of the combustion tube; and an additional injection unit located on the protrusion of the combustion tube and configured to inject fuel into the combustion tube.