A combustor includes: a fuel nozzle for injecting fuel; a combustion liner surrounding a combustion space for combusting the fuel and having an internal passage having an outlet communicating with the combustion space; and an air-fuel mixture line, connected to an inlet of the internal passage of the combustion liner, for introducing an air-fuel mixture containing the fuel and compressed air to the internal passage. The combustion liner is configured to be cooled by the air-fuel mixture flowing through the internal passage.