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 so that the irradiation position is changed in a surface direction of a fundus of the eye to change an imaging position on the eye at least between a first imaging region and a second imaging region different from the first imaging region in the surface direction of the fundus; and a detector for detecting an interference state between the measurement light reflected from the eye and reference light, and a displacement detecting unit provided to detect displacement in continuity in the surface direction of the fundus between a tomographic image having already been obtained in the first imaging region and a tomographic image to be obtained in the second imaging region changed by the irradiation position changing unit and different from the first imaging region in the surface direction of the fundus.