Apparatus and method for hemoglobin measurement including irradiating light to a living body, detecting light that has propagated through the living body, and acquiring measured data that represents a change in the concentration of oxidized hemoglobin in the living body and a change in the concentration of deoxidized hemoglobin; irradiating light to the living body, detecting light that has propagated through the living body, and acquiring measured data that represents a change in the concentration of oxidized hemoglobin in the living body and a change in the concentration of deoxidized hemoglobin; classifying the data measured at the first step and the data measured at the second step according to each of an increase or a decrease in the concentration of oxidized hemoglobin and an increase or a decrease in the concentration of deoxidized hemoglobin; and displaying the classifications determined at the third step.