A measurement method of measuring, as a spectroscopic characteristic, an absorption coefficient and a scattering coefficient inside of a scattering medium using diffuse optical tomography, said method comprising: a first step of irradiating light into the scattering medium and detecting diffused light as diffuse optical tomography data; a second step of irradiating light into the scattering medium, detecting modulated light as acousto-optical tomography data or elastic waves as photo-acoustic tomography data, and reconstructing (S100-S103), from these data, respectively a distribution of the spectroscopic characteristic using a physical model for acousto-optical tomography or a distribution of the absorption coefficient using a physical model for photo-acoustic tomography; and a third step of reconstructing (S104-S110) the spectroscopic characteristic of the scattering medium from the data obtained in the first step by an algorithm which repeatedly estimates a distribution of the spectroscopic characteristic inside of the scattering medium, calculates a predicted detection value of diffused light from the estimated distribution according to a physical model of light propagation, and calculates a difference between the predicted detection value and a detected value of diffused light obtained in the first step; wherein the algorithm uses the distribution obtained in the second step for at least one of an initial value for determining the estimated distribution, a constraint condition for assessing permissibility of the estimated distribution, or a boundary condition for fixing a spatial part of the estimated distribution, and stops repeating when the calculated difference falls within a permissible range (ε). a first step of irradiating light into the scattering medium and detecting diffused light as diffuse optical tomography data; a second step of irradiating light into the scattering medium, detecting modulated light as acousto-optical tomography data or elastic waves as photo-acoustic tomography data, and reconstructing (S100-S103), from these data, respectively a distribution of the spectroscopic characteristic using a physical model for acousto-optical tomography or a distribution of the absorption coefficient using a physical model for photo-acoustic tomography; and a third step of reconstructing (S104-S110) the spectroscopic characteristic of the scattering medium from the data obtained in the first step by an algorithm which repeatedly estimates a distribution of the spectroscopic characteristic inside of the scattering medium, calculates a predicted detection value of diffused light from the estimated distribution according to a physical model of light propagation, and calculates a difference between the predicted detection value and a detected value of diffused light obtained in the first step; wherein the algorithm uses the distribution obtained in the second step for at least one of an initial value for determining the estimated distribution, a constraint condition for assessing permissibility of the estimated distribution, or a boundary condition for fixing a spatial part of the estimated distribution, and stops repeating when the calculated difference falls within a permissible range (ε).