To improve performance characteristics such as a light condensing ratio and a flare attenuation so as to reduce diffuse reflection by comprising an optical detector assembly, a first plane mirror assembly, and a second plane mirror assembly, which are specified respectively.

A light condenser 100 used for condensing and detecting a radiation which is emitted from a scanned information medium so as to be reflected or transmitted is provided with an optical detector assembly 8, a first plane mirror assembly 2, and a second plane mirror assembly 3, which are constructed so as to maximize a light condensing ratio and a flare radiation attenuation. The lower ends of the first plane mirror assembly 2 and the second plane mirror assembly 3 are arranged at certain interval so as to form an opening, through which the radiation emitted from the information medium so as to be reflected and transmitted is passed. Each of the first plane mirror assembly 2 and the second plane mirror assembly 3 includes a regular reflection mirror provided with an acrylic substrate coated with a reflective aluminum coating by means of vacuum deposition. The beam discharged from the second opening of the light condenser 100 is gathered on a fluorescent material 9.