Burner, hydrogen generator, and fuel cell power generation system

A burner comprises a fuel distributor (1) having fuel injection holes (8), an air injector (2) having air injection holes (9) surrounding the fuel distributor, a temperature detector (6) having temperature detecting portion located within combustion space (3) in vicinity of air injection hole and a flame detector. A gap is formed between the temperature detector and the inner face of the air injection hole. A width of the gap is uniform over an outer periphery of the temperature detector.