To facilitate rough measurement by displaying lines representing a reference line or an angle to be a reference on the surface of a mirror so that a matter reflected by the mirror may be easily measured using the mirror because it may be a labor load that a tape measure or ruler is used in measurement of a matter.

A thin silver film which is indispensable to a mirror and is applied on the backside of a mirror is dare to be peeled off into a shape of an aimed reference line and light is applied from the backside of the mirror to display a line of light to be the reference on the surface of the mirror.