A lens for an optical recording and reproducing system includes: a plane of incidence on which a light generated from a light source is made incident; a first reflection side for reflecting a light passing through a plane of incidence; and a second reflection side for reflecting again the light that has been reflected on the first reflection side, the second reflection side being formed to be an ellipsoid side, and the first reflection side and the second reflection side being coated with a reflection material. A very small optical system in its size and weight is possibly constructed, so that information recording and reproducing can be possible only with one focussing lens without a necessity of an objective lens. Accordingly, an ultra-thin optical recording and reproducing system of which height is remarkably reduced can be provided. In addition, since the weight of the head portion can be reduced and the entrance pupil of the light source can be made small, a power consumption of a driving unit and an overall system can be much reduced.