A probe holder mounting device for a biological photometric device includes: a probe holder having a plurality of probe mounting parts to which optical fiber probes are mounted; a band-like mounting device body having a plurality of insertion holes into which the probe mounting parts are to be inserted to fix the probe holder in position by means of the insertion holes; belts whose one ends are respectively connected to both longitudinal ends of the mounting device body and whose other ends are engaged with each other; and an adjusting belt connected to the mounting device body at a position where the probe holder is fixed in position in a lateral direction of the mounting device body.