1. A stereo camera, comprising: an imaging device for capturing a stereo-image which comprises a pair of right and left parallax images; a fiducial light beam projector that projects a light beam to a subject to produce a fiducial mark on said subject; a fiducial mark detecting processor that detects image loci of said fiducial mark in said right and left parallax images; and a convergence adjusting processor that adjusts the convergence of said stereo-image in accordance with said image loci of said fiducial mark; wherein said fiducial light beam is emitted in a plane of symmetry which includes a perpendicular bisector line of a segment between viewpoints of said right and left parallax images.