An optical system, comprising: a light beam redirecting surface which functions to redirect light while transmitting the light and form a real image at a plane-symmetric position, and a mirror surface disposed facing the light beam redirecting surface; wherein an image of a subject of projection that has been disposed on an observation side opposite a side on which the mirror surface has been disposed across the light beam redirecting surface, is formed as if reflected in a virtual mirror that does not exist as a substantial body at a position that is in plane symmetry to the mirror surface with respect to the light beam redirecting surface to which the virtual mirror has been moved by transmitting light emitted from the subject of projection through the light beam redirecting surface, reflecting the transmitted light from the mirror surface, and again transmitting the reflected light through the light beam redirecting surface, the light beam redirecting surface is provided in an optical element, characterized by comprising: a reflective plane-symmetric imaging element formed from a plurality of unit optical elements, each of said unit optical elements being provided with two mirrored surface elements mutually perpendicular to each other, arranged on a plane; wherein, light transmitted from one side to the other side of the light beam redirecting surface of the reflective plane-symmetric imaging element is reflected once by each of the two mirrored surface elements of each unit optical element, and the light beam redirecting surface is a light beam redirecting surface that passes alongside the two mirrored surface elements and is disposed perpendicularly or at an angle close to perpendicular with respect to the two mirrored surface elements. a light beam redirecting surface which functions to redirect light while transmitting the light and form a real image at a plane-symmetric position, and a mirror surface disposed facing the light beam redirecting surface; wherein an image of a subject of projection that has been disposed on an observation side opposite a side on which the mirror surface has been disposed across the light beam redirecting surface, is formed as if reflected in a virtual mirror that does not exist as a substantial body at a position that is in plane symmetry to the mirror surface with respect to the light beam redirecting surface to which the virtual mirror has been moved by transmitting light emitted from the subject of projection through the light beam redirecting surface, reflecting the transmitted light from the mirror surface, and again transmitting the reflected light through the light beam redirecting surface, the light beam redirecting surface is provided in an optical element, characterized by comprising: a reflective plane-symmetric imaging element formed from a plurality of unit optical elements, each of said unit optical elements being provided with two mirrored surface elements mutually perpendicular to each other, arranged on a plane; wherein, light transmitted from one side to the other side of the light beam redirecting surface of the reflective plane-symmetric imaging element is reflected once by each of the two mirrored surface elements of each unit optical element, and the light beam redirecting surface is a light beam redirecting surface that passes alongside the two mirrored surface elements and is disposed perpendicularly or at an angle close to perpendicular with respect to the two mirrored surface elements. a reflective plane-symmetric imaging element formed from a plurality of unit optical elements, each of said unit optical elements being provided with two mirrored surface elements mutually perpendicular to each other, arranged on a plane; wherein, light transmitted from one side to the other side of the light beam redirecting surface of the reflective plane-symmetric imaging element is reflected once by each of the two mirrored surface elements of each unit optical element, and the light beam redirecting surface is a light beam redirecting surface that passes alongside the two mirrored surface elements and is disposed perpendicularly or at an angle close to perpendicular with respect to the two mirrored surface elements.