A biological measurement device includes a phase modulation type interferometer, a first stage, a light transmitting plate, and a second stage. The first stage is able to retain a target which is a biological body. The light transmitting plate is disposed between the first stage and the interferometer in a direction of an optical axis of measurement light of the interferometer. The second stage supports the light transmitting plate. The first stage is configured to expand by a pressure of a gaseous body in the direction of the optical axis of the measurement light of the interferometer and to press the target against the light transmitting plate.