Provided is a method for generating a distribution image showing the molar concentration ratio of first and second biological substances contained in biological tissue for which the absorption spectrum in a prescribed wavelength band has, in order from the short wavelength end, a first, second, third, and fourth isosbestic points, wherein the method includes: a step of using light isolated from white light by a first optical filter that collectively selectively isolates light of a first wavelength band demarcated by the first isosbestic point and the second isosbestic point, a second wavelength band demarcated by the second isosbestic point and the third isosbestic point, and a third wavelength band demarcated by the third isosbestic point and the fourth isosbestic point, to capture an image of the biological tissue and acquire first imaging data G1 a step of using light isolated from white light by a second optical filter that selectively isolates light of the second wavelength band to capture an image of the biological tissue and acquire second imaging data G2 and a step of generating a distribution image on the basis of the first imaging data G1 and the second imaging data G2.
