A biological photometric device, comprising: at least one light irradiating unit (50, 101) and a plurality of light detecting units (60, 102) or a plurality of light irradiating units (50, 101) and at least one light detecting unit (60, 102), wherein the at least one or the plurality of light irradiating units (50, 101) are adapted to irradiate light on a subject, and the at least one or the plurality of light detecting units (60, 102) are adapted to detect the light, which is irradiated on an irradiation point on the subject from the at least one or the plurality of light irradiating units (50, 101) and propagated in the subject, at a detection point on the subject; and an analysis part adapted to analyse the signal obtained by the at least one or the plurality of light detecting units (60, 102); wherein the light irradiating and detecting units (50, 101, 60, 102) are respectively disposed on the subject such that at least two different SD distances are set, each SD distance being defined on the subject as a distance between the irradiation point and the detection point, and the analysis part is adapted to extract one or a plurality of separated signal components using a signal separation method from the plurality of measurement data measured by combinations of the light irradiating and detecting units (50, 101, 60, 102) and reconstruct modified measurement data; characterised in that the analysis part is adapted to select the separated signal components on the basis of a gradient in the SD distance dependency of the signal components and reconstruct the modified measurement data using the selected separated signal components, and the gradient in the SD distance dependency is a model parameter of a regression curve obtained by performing regression analysis for a functional value determined by at least one of an amplitude value, an amplitude value standard deviation, and a weight value at each measurement point of the one or the plurality of separated signal components, by using the SD distances or a partial optical path length in the gray matter of the subject's brain. at least one light irradiating unit (50, 101) and a plurality of light detecting units (60, 102) or a plurality of light irradiating units (50, 101) and at least one light detecting unit (60, 102), wherein the at least one or the plurality of light irradiating units (50, 101) are adapted to irradiate light on a subject, and the at least one or the plurality of light detecting units (60, 102) are adapted to detect the light, which is irradiated on an irradiation point on the subject from the at least one or the plurality of light irradiating units (50, 101) and propagated in the subject, at a detection point on the subject; and an analysis part adapted to analyse the signal obtained by the at least one or the plurality of light detecting units (60, 102); wherein the light irradiating and detecting units (50, 101, 60, 102) are respectively disposed on the subject such that at least two different SD distances are set, each SD distance being defined on the subject as a distance between the irradiation point and the detection point, and the analysis part is adapted to extract one or a plurality of separated signal components using a signal separation method from the plurality of measurement data measured by combinations of the light irradiating and detecting units (50, 101, 60, 102) and reconstruct modified measurement data; characterised in that the analysis part is adapted to select the separated signal components on the basis of a gradient in the SD distance dependency of the signal components and reconstruct the modified measurement data using the selected separated signal components, and the gradient in the SD distance dependency is a model parameter of a regression curve obtained by performing regression analysis for a functional value determined by at least one of an amplitude value, an amplitude value standard deviation, and a weight value at each measurement point of the one or the plurality of separated signal components, by using the SD distances or a partial optical path length in the gray matter of the subject's brain.