To provide an optical sheet and a method for manufacturing the sheet having cone-like projections, excellent optical characteristics and good reproducibility of the form of dies and avoiding such drawback that the tops of projections easily chip, and to provide a surface light source device and a display device.

The optical sheet 1 consists of a transparent base film 2 and a great number of cone-like projections 3 with the tops 4 each forming a part of a sphere and densely arranged on the film 2. The projection has 20 to 300 μm diameter L of the bottom, 5 to 200 μm height and the ratio r/L of the radius r of the sphere to the diameter L ranging from 0.05 to 0.4.