1. An imaging device comprising: a plurality of photoelectric conversion elements arranged in a matrix at intersections of a plurality of row selection lines and a plurality of column selection lines crossing at right angles on a substrate: a horizontal scanning circuit for sequentially selecting each of the row selection lines from a start row selection line at one end of the substrate to an end row selection line at the other end of the substrate to perform line exposure of all of the photoelectric conversion elements arranged in the selected row selection line, to thereby cause each of the photoelectric conversion elements to produce a photoelectric converted pixel signal; a vertical scanning circuit for sequentially selecting each of the plurality of column selection lines while the horizontal scanning circuit selects any of the row selection lines to read out the pixel signal of the photoelectric conversion element disposed at an intersection between the selected row selection line and the selected column selection line, the horizontal scanning circuit and the vertical scanning circuit selecting all of the row section lines and the column selection lines by a progressive method at each frame period in synchronization with an output period of a moving image; an image sensor for producing a frame image by synthesizing the pixel signals which are read out of the respective photoelectric conversion elements disposed at the intersections of all the selected row selection lines and all the selected column selection lines; moving image production section for producing the moving image on the basis of a sequence of the frame images which are sequentially synthesized; and moving image output section for outputting the moving image with a predetermined output period, wherein the horizontal scanning circuit selects as the start row selection line one of a first start row selection line and a second start row selection line, which is disposed between the first start row selection line and the end row selection line, with a switching period longer than the output period in an alternate manner at a start time in synchronization with the frame period, and the moving image production section extracts a first common frame image, which is synthesized from the pixel signals that the photoelectric conversion elements arranged in the row selection lines from the second start row selection line to the end row selection line produce by photoelectric conversion, from a first frame image synthesized by the image sensor in each frame period with the first start row selection line set as the start row selection line, and produces the moving image, which is a sequence of the first common frame image and second frame images synthesized by the image sensor in each frame period with the second start row selection line set as the start row selection line.