1. An imaging apparatus comprising: a planar image acquisition unit configured to acquire a planar image of a subject; a splitting unit configured to split light generated by a light source into a measuring beam for a tomographic image of the subject and a reference beam; a tomographic image acquisition unit configured to acquire the tomographic image based on a combined beam obtained by combining the reference beam and a return beam from the subject irradiated with the measuring beam for the tomographic image; a branch unit configured to branch into an optical path of a measuring beam for the planar image and an optical path of the measuring beam for the tomographic image, the branch unit being disposed closer to the subject than the splitting unit; and a polarization adjustment member configured to adjust polarization states of the measuring beam for the planar image and the measuring beam for the tomographic image, the polarization adjustment member being disposed closer to the subject than the branch unit in a common optical path of the optical path of the measuring beam for the planar image and the optical path of the measuring beam for the tomographic image.