A device is provided for the optical measurement of a living body. For the purpose of separating a signal coming from the change in hemodynamics in a deep part from a signal coming from the change in hemodynamics in skin, light irradiation sites and light detection sites are positioned so that the measurement is achieved employing at least two SD distances. At two SD distances, the change in a logarithmic value of the detected light at every time point is determined employing a logarithmic value of the amount of detected light under specific conditions or at a specific time point as a starting point. A gradient value for a differential SD distance, which is a difference between the amount of change obtained by the measurement at a longer SD distance and the change obtained by measurement at a shorter SD distance, is used as a measurement amount.
