A biological observation apparatus according to the present application includes a sound wave radiating unit that radiates a sound wave into an object to be examined in living tissue, a light radiating unit that radiates light into the object, a light interfering unit that makes the light radiated from the light radiating unit interfere with light reflected from an area where the sound wave reaches and radiates interference light, a light detector that detects the interference light radiated from the light interfering unit and outputs an interference signal corresponding to the interference light, and a calculation unit that calculates the amount of frequency modulation of the radiated light based on the interference signal outputted from the light detector and calculates a difference value between the two adjacent amounts of frequency modulation in sequence.