1. An image pickup apparatus comprising: a lens array placed at a position facing a subject to be taken and having a plurality of lenses arranged in an array, a part of the lenses making one or more stereo lens pairs; an image pickup device placed on a side of an image plane of the lens array and configured to take a multifaceted compound-eye image consisting of a set of monocular images formed by the plural lenses; and a computing unit for computing range imagery from one or more pairs of the monocular images formed by said one or more stereo lens pairs, wherein the computing unit includes imaging position determination means for determining from the monocular images an image pickup position of each of one or more of the subjects whose relative positional relationships with respect to the image pickup apparatus are known; and image distortion parameter determination means for determining an image distortion parameter based upon a determination result of the imaging position determination means; wherein the imaging position determination means divide the multifaceted compound-eye image taken by the image pickup device into the monocular images and detect from the monocular images said one or more subjects with known relative positional relationships, and the image distortion parameter determination means determine the distortion parameter based upon a detected position of each of the determined subjects to correct the distortion of each of the monocular images using the distortion parameter.