There is provided an optical bioinstrumentation device, with which measurement data reflect more correctly the information inside the living body with less noise even the subject moves when the information inside the living body is measured by using the light.In the present invention, the means for fixing the part other than the tips of the optical fibers for irradiation and detection on the fixing member which is to fix the tips of the optical fiber for irradiation and detection on the subject, or, the means for fixing the optical fiber is fixed on the fixing member which is to fix the end of the optical fiber on the subject, or the means for fixing the optical fiber at two or more positions on the subject.