Provided is an optical measurement apparatus to which a measurement probe having an illumination fiber and a light receiving fiber is configured to be detachably connected and which is configured to perform optical measurement on a measurement target. The optical measurement apparatus includes: a light source unit configured to emit illumination light to the measurement target via the illumination fiber; a light receiving unit configured to receive light propagated via the light receiving fiber; and a calculation unit configured to calculate a characteristic value of a measurement history of each of the illumination light and external light incident from outside, based on a plurality of measured values obtained by receiving diffused light of the illumination light reflected from a reflection index member and on a plurality of measured values obtained by receiving diffused light of the external light that has been transmitted through a diffusion index member as uniform light.