A pulse wave measuring apparatus is disclosed, in which a sensor unit can be fixed easily under an appropriate pressure at an appropriate position on a living organism. With the living organism fixed by a living organism fixing device, a pressure sensitive portion arranged on the sensor unit is pressed against the living organism thereby to measure the pulse wave. The living organism fixing device includes a fixing stand for fixing the living organism in position, and fastening bands for connecting the fixing stand and the sensor unit and fastening the living organism fixedly to the fixing stand while at the same time activating by pressing the sensor unit against the living organism. The fastening bands include a first band portion with one end mounted on the sensor unit and the other end mounted on the fixing stand and a second band portion with one end mounted on the sensor unit and the other end removably mounted on the fixing stand. The fixing stand has a constant force spring for pulling the other end of the first band portion with a constant force.