1. A single-eye stereoscopic imaging device comprising: a single imaging optical system which includes a focus lens; an imaging element which acquires a plurality of images by receiving light beams which each pass through different regions of the imaging optical system; an aperture where it is possible to change an aperture value; distance information acquiring unit which determines a distribution of distance information on subjects which are included in the plurality of images based on the plurality of images; and control unit which controls the aperture value and movement of the focus lens such that a parallax amount of an image region, which is a target of parallax adjustment, is a parallax amount within a predetermined range based on the distribution of the distance information.