An optical sheet for a backlight is provided on a surface light source in the backlight. An optical reflection layer has a plurality of through grooves formed on a transparent substrate and arranged at a prescribed interval. The width of the through hole is narrowed from the upper surface opening to the lower surface opening. Each of the cylindrical lenses is filled within a corresponding through groove, and its surface is a cylindrical surface that covers the upper surface opening of the through groove. Light from the light source comes in only from the lower surface opening, so that the angle of incidence of light when the light reaches the cylindrical surface can be controlled, and an increased amount of light deflected toward the front surface can be emitted. Therefore, the optical sheet for a backlight can collect light from the surface light source in the front surface direction.