1. An imaging apparatus, comprising: a plurality of optical systems; a plurality of imaging regions in one-to-one correspondence with the plurality of optical systems, each of the imaging regions including a plurality of pixels arranged in a two-dimensional matrix, the plurality of imaging regions being disposed in a matrix along a direction substantially parallel to an array direction of the plurality of pixels included in the imaging regions, and each of the imaging regions being disposed on an optical axis of the respective optical systems on a one-to-one basis; an origin assigning unit configured to assign respective origins of the respective imaging regions based on respective intersections of the respective optical axes of the respective optical systems and the respective imaging regions corresponding thereto without movement of the origins and the imaging regions depending on a distance of a subject, a line connecting two of the assigned respective intersections of adjacent imaging regions disposed in the matrix being not parallel to the array direction of the plurality of pixels of at least one of the adjacent imaging regions; a pixel position specifying unit configured to specify positions of the plurality of pixels of the respective imaging regions using the respective origins as references; and a parallax detecting unit configured to detect parallax using the pixel position of the subject in a first image of the subject captured by one of the imaging regions and the pixel position of the subject in a second image of the subject captured by one of the imaging regions.