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, wherein the distance information acquiring unit divides the standard image which is one image out of a plurality of images into a plurality of regions, calculates the distance information for each of the plurality of divided regions, divides the distance information into a plurality of classes for each distance range, and creates a histogram where the number of regions, where the distance information which is calculated falls in the ranges of each of the classes, is the frequency; 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.