A displacement measurement method, an apparatus thereof, and a probe microscope. which enable stable measure an amount of displacement and a moving distance of an object under measurement with an accuracy of the sub-nanometer order or below without being affected by disturbances such as fluctuations of air and mechanical vibration. A pulsed beam is split into two; one beam is reflected by an object under measurement and then inputted to a delay optical path equivalent to one pulse period; and the other beam is sent through the same delay optical path in the opposite direction up to the object under measurement with a delay of one pulse period, and then reflected by the object under measurement. An optical phase variation caused by the movement of the object under measurement is obtained by subjecting the two pulsed beams to interference.