An optical tomographic imaging apparatus (100), method and program are provided which include 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 (100) according to the present invention captures an optical interference tomographic image based on a combined beam (142) that combines a return beam (108) from an object (107) irradiated by a measuring beam (106) and a reference beam (105) corresponding to the measuring beam (106). The imaging apparatus according to the present invention further includes a beam diameter changing unit (136) for changing a beam diameter of the measuring beam (106). Furthermore, the imaging apparatus according to the present invention includes a detection unit (150) configured to detect the combined beam (142) at a resolution according to the beam diameter.
