A signal processor includes: a phase matching section adapted to bring two image signals supplied from two cameras into phase, one image signal being a left image signal and the other image signal being a right image signal; a phase adjustment section adapted to change the horizontal phase of the left and/or right image signal based on a phase displacement so as to move both or either of the left and right images horizontally by a predetermined distance and output the image signals with changed parallax between the left and right images; and a read section adapted to output the left and/or right image signal in which, of those areas displayed three-dimensionally and other areas where only the left or right image is displayed two-dimensionally, the image in the two-dimensionally displayed areas has been replaced by an image different from that in the three-dimensionally displayed areas.