1. A range-finding device comprising a plurality of two-dimensional image pickup units disposed at a predetermined interval with each other; 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 distance calculation unit configured to calculate a distance to the subject based on the signals output from the image pickup units, wherein the plurality of image pickup units are formed on a single substrate, 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 distance calculation unit 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.