Light P of a predetermined wavelength irradiates one light incident position I set on the surface Ba of a scattering-absorption body B. The light P that propagates through the interior of the scattering-absorption body B is detected at one light detecting position D set on the surface Ba of the scattering-absorption body B, to yield a light detection signal. On the basis of this light detection signal, a temporal profile of the light intensity of the detected light is acquired, and on the basis of the temporal profile, an mean optical path length L of the light P in the interior of the scattering-absorption body B and information relating to the amount of substance to be measured in a region to be measured B1 are calculated. The information relating to the amount of substance to be measured is corrected on the basis of the mean optical path length L, such that the longer the mean optical path length L, the greater the amount of substance to be measured is. The method allows obtaining measurement results, exhibiting no influence of intervening tissue, to be obtained in accordance with a simple method.
