The ophthalmologic apparatus 1 splits low coherence light LO into a signal light LS and a reference light LR, the interference light LC being generated by having the signal light LS overlap with the reference light LR, and detects this interference light LC. In addition, the apparatus comprises an optical alignment system 190A for performing the alignment of an optical system forming the signal light path to the eye E. An intraocular distance calculator 214 determines the distance between the position where the signal light LS has been introduced onto the eye E and the position where the signal light LS has been reflected by the fundus oculi E based on length of the optical path of the signal light, the length of the optical path of the reference signal light, the working distance after alignment, and the detection signal output by the CCD 184 (or signal intensity data).
