PURPOSE: To improve distance sense as effectively as possible by using the concave face of a curved face obtained by mutually rotating two same curved faces obtained by cutting out squares from the side of a right circular cylinder in parallel with its axis by 90° as a mirror.

CONSTITUTION: A mirror using the inside of a horizontal right circular cylinder as a reflecting face in parallel with its axis so as to be a half or less and a horizontal right circular cylinder inside mirror 1 cut out rectangularly to a square plane and a vertical right circular cylinder inside mirror 2 obtained from a vertically arranged right circular cylinder are obtained. The concave inside of a composite curved face obtained by composing the curved faces of both the mirrors 1, 2 are used as reflecting faces to obtain a concave composite curved face mirror. The concave composite curved face mirror is improved at its distance sense and can be easily observed as compared with a concave mirror.