A calibration apparatus includes an insertion portion into which a measurement probe is inserted and a reference reflection plate that is arranged at a position away from a distal end of the measurement probe by a predetermined distance in a state in which the measurement probe has been inserted in the insertion portion and that has uniform reflectivity of light in a range of a wavelength to be measured in an irradiation plane of an illumination light, wherein a material forming the reference reflection plate has a scattering mean free path that is greater than a spatial coherence length at the predetermined distance.
