A light diffusing sheet capable of changing a backward and forward diffusing ability and a right and left diffusing ability to be adapted to both luminance distribution in a direction perpendicular to a lamp and luminance distribution in the direction parallel to the lamp, and thereby increasing light emanating in a normal direction in either direction and a back light unit using the light diffusing sheet. A light diffusing sheet 1 for use in a back light unit of a liquid crystal display includes light diffusing means which has a backward and forward diffusing ability and a right and left diffusing ability that differ from each other. The light diffusing means includes longitudinally divided spindle shaped convex regions or concave regions formed on a sheet surface, quadrangular pyramid shaped convex regions or concave regions each having a rectangular bottom surface, spindle-shaped light diffusing material dispersed in the sheet with central axes thereof directed in a backward and forward direction or in a right and left direction, and a light diffusing layer in which the spindle-shaped light diffusing materials is dispersed.