First image forming part forms a two-dimensional surface image of a fundus oculi of an eye based on optically obtained data. Second image forming part forms tomographic images of fundus oculi based on data obtained by optically scanning a region of the surface of fundus oculi corresponding to at least part of two-dimensional image. Accumulated image generating part generates an accumulated image by accumulating the formed tomographic images in a depth-wise direction. Extracting part extracts first vascular territory corresponding to a fundus oculi vessel from two-dimensional image formed by first image forming part, and also extracts second vascular territory corresponding to a fundus oculi vessel from accumulated image generated by accumulated image generating part. Specification part specifies a position of a vascular cross sectional region corresponding to a cross section of a fundus oculi vessel in the tomographic image based on extracted first vascular territory and extracted second vascular territory.