1. An optical coherence tomography apparatus for selectively visualizing and analyzing a vascular network in a choroidal layer comprising an optical coherence tomography device, and a computer that obtains three-dimensional OCT tomographic images based on OCT-measured data acquired by the optical coherence tomography device and processes three-dimensional OCT tomographic images; said optical coherence tomography apparatus for selectively visualizing and analyzing a vascular network in a choroidal layer characterized in that: the computer functions as a means for selectively separating out only images of choroidal vessels from the three-dimensional OCT tomographic images to obtain image data of the choroidal vessels, and also as a means for obtaining data to be used in a quantitative evaluation of a shape of the choroidal vessels based on image data of the choroidal vessels; and the means for acquiring image data of the choroidal vessels is constituted in such a way that tomographic image data of the choroidal layer is extracted from OCT-measured data, the tomographic image data of the choroidal layer is sliced at equally pitched positions in a depth direction of the choroidal layer and data of image slices is extracted, after which image data of the choroidal vessels is obtained from data of image slices.