1. A range-finding device comprising a plurality of two-dimensional image pickup units formed on a single substrate and disposed at a predetermined interval with each other, wherein each of the image pickup units comprises a plurality of light receiving elements, and wherein adjacent ones of the image pickup units are separated by a region of sufficient width that the substrate can be cut at a location between the image pickup units; a lens unit configured to form subject images of a subject on the plurality of image pickup units, the image pickup units on which the subject images are formed outputting signals of the subject images; and a calculator to calculate a distance to the subject based on the signals output from the image pickup units, wherein the subject images are formed through the lens unit on at least two image pickup units of the plurality of image pickup units, and the calculator is configured to calculate a distance to the subject based on the signals output from the at least two image pickup units on each of which the subject image is formed, wherein the lens unit has a lens array and a plurality of lenses integrally formed on the lens array and disposed so as to face the plurality of image pickup units, the plurality of lenses are two lenses arranged in a row so as to respectively face two both side image pickup units of the plurality of image pickup units between which at least one image pickup unit is disposed, and no further lens is provided at a center area corresponding to at least one of the image pickup units which is disposed between the two both sides image pickup units.