To provide an optical sheet capable of efficiently taking light from a light source from the back surface thereof at a certain angle other than the front, a backlight unit and a display device.

The optical sheet 10 includes a light reflecting layer 4, a photosensitive adhesive layer 5, a base (base sheet) 6, and an optical element part having lenses 7 (optical elements) aligned thereon in order from the back surface side thereof. The light reflecting layer 4 includes an optical opening 8A transmitting the light and a light reflecting part 8B reflecting the light, which are alternately aligned in the alignment direction of the lenses 7. The optical opening 8A is located in a position opposed to each lens 7 to regulate the incident light onto the lens 7. When the optical sheet 10 is viewed in a direction orthogonal to the alignment direction of the lenses 7 and orthogonal to the thickness direction of the optical sheet 10, a center line T2 passing through the center of the optical opening 8A opposed to each lens 7 is displaced relative to a center line T1 passing through the apex of the lens 7.