A dual-wavelength thermal infrared sensor includes a first and a second type pixels that detect infrared in different wavelength ranges. The pixels of both types include a diaphragm supported by beams, an eave formed to spread outward from the diaphragm, and reflection film on the substrate. The diaphragm includes a thermoelectric conversion material thin film, an electrode, and protective films. The protective films and eaves are made of a material having larger absorption coefficient for infrared in the first wavelength range and a smaller absorption coefficient for infrared in second wavelength range. First-type pixels further have metal thin films formed on the top of the diaphragm and eaves. First-type pixels have sensitivity to infrared in a first wavelength range and in a second wavelength range defined by optical interference occurring between the metal thin films and the reflection film. Second-type pixels have sensitivity to first wavelength range infrared.