The present invention provides an optical axis compensator, which comprises a liquid sealing container 1 with a transparent liquid 14 sealed therein so as to form a free liquid surface 2, an optical axis compensating unit 44 for allowing a light beam to pass through the liquid sealing container at a predetermined angle and for performing optical axis compensation based on changes of an exit optical axis according to angular change of said free liquid surface with respect to an incident optical axis, a tilting mechanism 12 for tilting said optical axis compensating unit, tilt detecting means for detecting tilt of said optical axis compensating unit, and a control unit for driving said tilting mechanism according to a signal from said tilt detecting means and for leveling said optical axis compensating unit, whereby said control unit drives said tilting mechanism according to tilt detection from the tilt detecting means and levels the optical axis compensating unit, and the optical axis compensating unit compensates a tilt angle of the optical axis.