1. A stereoscopic imaging apparatus comprising: a single photographing optical system; an image sensor for forming images from pupil-split object images which had passed through a first and a second regions of the photographing optical system with each region in a predetermined different direction, and the image sensor photo-electrically converts the object images which had passed through the first and the second regions to output a first image and a second image; an AF image selecting part for selecting the image from the first or the second images to be used for contrast AF; and a contrast AF controlling part for controlling the positions of a lens in the photographing optical system by using the image selected with the AF image selecting part in order to maximize an image contrast in a predetermined AF area of the image.