Flame detector

A first bandpass filter selects and transmits light of flame with own infrared wavelength. A first infrared receiving element receives light from the first bandpass filter. A second bandpass filter selects and transmits light with an infrared wavelength, wherein the infrared wavelength is not the own one of the flame. A second infrared receiving element receives light from the second bandpass filter. A first output of the first infrared receiving element is compared with a second output of the second infrared receiving element, to detect the flame. When light incidence with even energy is present on the first bandpass filter and the second bandpass filter in the transmission wavelength ranges of the first bandpass filter and the second bandpass filter, the quantity of the transmitted light through the second bandpass filter is smaller than that through the first bandpass filter, and the first output and the second output are adjusted to cause that the level of the first output is equal to that of the second o