1. An ophthalmic photographing apparatus arranged to obtain an image of an examinee's eye, the apparatus comprising: a photographing unit comprising an interference optical system comprising a first light source and arranged to divide light from the first light source into measurement light and reference light, guide the reference light to a reference optical system, guide the measurement light to a projection optical system arranged to scan a given portion of the eye with the measurement light, and combine the measurement light reflected from the given portion and the reference light into interference light by using a light combining member, and arranged to make the interference light enter a photodetector to obtain a tomographic image of the given portion; an observation unit comprising a projection optical system comprising a second light source and arranged to illuminate the given portion with illumination light emitted from the second light source, and a photo-receiving optical system arranged to make the illumination light reflected from the given portion enter a photo-detector, and arranged to obtain a front image for observation of the given portion; a photographing control unit arranged to control operation of the photographing unit to scan an X-Y scanning region of the given portion and obtain information on a three-dimensional image; an image information processing unit arranged to (a) process the three-dimensional information to obtain an interference front image based on one of accumulation information in a depth direction and image information on a surface portion of the given portion, and (b) using the front image for observation as a reference image, compare the reference image and the interference front image to detect a positional deviation; and display means arranged to display the detected positional deviation information.