A fuel combustion apparatus 2 according to the present invention includes: a combustion cylinder 4; a fuel feed unit 6 that introduces a swirling flow of an air-fuel mixture into the combustion cylinder; an ignition unit 10 including an igniter 32 located in the combustion cylinder 4; an ion detection unit 12 including a detector 40 located in the combustion cylinder 4; and a control unit 14 that adjusts a mixing ratio of the fuel based on a detection result obtained by the ion detection unit 12. Preferably, the fuel is ammonia. Preferably, the detector 40 is located in the vicinity of the igniter 32.