An optical tomographic imaging apparatus is provided which includes a low-resolution mode for rough imaging and a high-resolution mode for obtaining detailed images. In particular, an optical tomographic imaging apparatus is provided which enables tomographic imaging during a high-resolution mode to be performed at higher speeds. An imaging apparatus according to the present invention captures an optical interference tomographic image based on a combined beam that combines a return beam from an object irradiated by a measuring beam and a reference beam corresponding to the measuring beam. The imaging apparatus according to the present invention further includes a beam diameter changing unit for changing a beam diameter of the measuring beam. Furthermore, the imaging apparatus according to the present invention includes a detection unit configured to detect the combined beam at a resolution according to the beam diameter.
