A fundus oculi observation device 1 has a function of forming a tomographic image of a fundus oculi Ef and a function of capturing a two-dimensional image of the surface of the fundus oculi Ef (a fundus oculi image Ef). An arithmetic and control unit 200: specifies a vascular region in the tomographic image and a vascular region in the fundus oculi image Ef obtains a common region of the vascular region in the tomographic image and the vascular region in the fundus oculi image Ef and specifies the common region in the tomographic image erases an image of the common region from the tomographic image and estimates a layer position within the common region to add an image representing this layer position to the common region and obtains the layer thickness of the fundus oculi Ef in the common region based on the image representing this layer position.
