Disclosed is a prism sheet structure that can control optical coupling between contact surfaces of two prism sheets in a backlight unit. The prism sheet includes: a structural surface (14) having non-planar peaks (11) with maximum height and minimum height along a length direction thereof; and a curved layer (17) having the same cycle as a cycle of height variation of the peak. The curved layer is formed at a boundary surface (16) between the structural surface 14 and the flat surface to maintain the right-angled isosceles triangular prisms formed due to a difference between the highest point and the lowest point of each of the peaks to have a predetermined size, so that distance between the valleys (12) is uniform along the length direction. Although shapes of prisms are identical, the cycle of the peak height variation allows the moire patterns to be suppressed or removed.