To acquire information relating to a vessel wall thickness by: acquiring interference signal sets of a plurality of frames including interference signal sets corresponding to a plurality of frames forming an image of the same cross section of an fundus； generating 3-D tomographic image data on the fundus from the interference signal sets of the plurality of frames； generating 3-D motion contrast data in the fundus from the interference signal sets corresponding to the plurality of frames that form the same cross section； extracting a vessel from the fundus based on the 3-D tomographic image data or the 3-D motion contrast data； detecting a coordinate of an outer surface of a vessel wall of the vessel based on the 3-D tomographic image data； and detecting a coordinate of an inner surface of the vessel wall of the vessel based on the 3-D motion contrast data.
