1. An ophthalmic photographing apparatus comprising: an optical coherence tomography device provided to imaging a tomographic image of an examinee's eye, the device including: an irradiation position changing unit for changing an irradiation position of measurement light emitted from a light source on the eye to change an imaging position on the eye; and a detector for detecting a interference state between the measurement light reflected from the eye and reference light, and a displacement detecting unit provided to detect displacement in continuity between a tomographic image having already been obtained in a first imaging region and a tomographic image to be obtained in a second imaging region different from the first imaging region.