This combustion device is provided with: a combustion tube (13) inside which is formed a combustion chamber (11); a fuel injector (15) for injecting fuel (F) and air (A) into the combustion chamber, the fuel injector being provided at the top of the combustion tube, and having a fuel injection member (34) that includes a plurality of fuel injection annular parts (33) and an air guide member (36) that includes a plurality of combustion-air annular parts (35) for guiding air for combustion, the fuel combustion annular parts and the combustion-air annular parts being disposed concentrically with each other; and a reheating burner (10) disposed in the downstream region of the combustion chamber, on the circumferential wall of the combustion tube. The fuel injection annular parts have a plurality of fuel injection holes (39) opening in the radial direction thereof, and have a plurality of air guide grooves (41) opening in the axial direction thereof, for guiding air to the fuel injected through the fuel injection holes.