An OCT apparatus of an exemplary aspect includes an OCT scanner, image data generating unit, registration unit, and image data composing unit. The OCT scanner is configured to acquire three dimensional data sets by applying an OCT scan to mutually different three dimensional regions of a sample. The image data generating unit is configured to generate a plurality of pieces of image data from the three dimensional data sets. The registration unit is configured to perform a first registration between the plurality of pieces of image data by applying an image correlation calculation to each of overlap regions in the plurality of pieces of image data. The image data composing unit is configured to compose the plurality of pieces of image data based on a result of the first registration.