Provided is a burner of double tube structure including an outer tube and an inner tube. The inner tube includes a tip-side support portion fixed on the outer tube, a base-side support portion fixed on the outer tube, a main body portion supported by the tip-side support portion, bellows interposed between the main body portion and the base-side support portion, and a bulkhead member attached at a position between the tip-side support portion and the base-side support portion. Between an outer peripheral surface of the bulkhead member and an inner peripheral surface of the outer tube, a second gap smaller than a first gap between an outermost peripheral surface of the bellows and the inner peripheral surface of the outer tube is interposed.