A concentration measurement apparatus includes a probe 20, having a light incidence section making measurement light incident on the head and a light detection section detecting the measurement light that has propagated through the interior of the head, and a CPU 14 determining temporal relative change amounts of oxygenated hemoglobin concentration and deoxygenated hemoglobin concentration and determining a correlation coefficient of the relative change amounts and a polarity of a slope of a regression line. A concentration measurement apparatus and a concentration measurement method that enable evaluation of the accuracy of calculation and the possibility of reverse direction blood transmission from the vena cava to the head based on the phase shift between the oxygenated hemoglobin concentration and the deoxygenated hemoglobin concentration are thereby realized.
