The present invention provides a wavelength detection device (10) provided with: a plurality of optical filters (12a, 12b); a splitting unit (11) which splits light and allows the split light to pass through each of the plurality of optical filters (12a, 12b); a plurality of light receiving elements (13a, 13b) which detect the intensities of different beams of light which have passed through the optical filters, respectively; and a calculation unit (16) which calculates, from the outputs of the plurality of light receiving elements, physical quantities related to the transmittances of the plurality of optical filters, and calculates the wavelengths of the beams of light which have passed through the plurality of optical filters, on the basis of the transmittance characteristics, wherein the transmittance characteristics of the plurality of optical filters have an inclination section in different wavelength ranges of the wavelength range of the object to be measured.