A biological optical measurement instrument has a gain adjustment unit (40) configured to set the gain value according to the intensity of the passing light in the measurement data detected by the optical measurement unit (12), a gain storage unit (44) configured to store the damage gain value set by the gain adjustment unit (40) when a damaged incident optical fiber (6a) or a damaged detection optical fiber (8a) is used, a gain comparison unit (42) configured to compare the gain value set by the gain adjustment unit (40) and the damage gain value stored in the gain storage unit (44), and a damage determination unit (46) configured to determine whether or not the incident optical fiber (6a) or the detection optical fiber (8a) is damaged on the basis of the comparison result by the gain comparison unit (42).The display unit (36) displays the damage condition.
