Triangular pyramid type cube-corner retroreflective element

A triangular-pyramidal cube-corner retroreflective element characterized in that triangular-pyramidal cube-corner retroreflective elements protruded onto a common bottom plane (Sx-Sx′) share a base edge (x) on the bottom plane and are arranged on the bottom plane (Sx-Sx′) in the closest-packed state so as to be faced each other, the bottom plane (Sx-Sx′) is a common plane including many base edges (x,x, . . . ) shared by the triangular-pyramidal reflective elements, two faced triangular-pyramidal reflective elements include the shared base edges (x,x, . . . ) on the bottom plane (Sx-Sx′) and form a pair of substantially-same-shaped elements faced each other so as to be substantially symmetric to planes (Lx—Lx, Lx—Lx, . . . ) vertical to the bottom plane (Sx-Sx′), and the optical axis of the triangular-pyramidal reflective element pair tilts so that the angle formed between the optical axis and a vertical line extended from apexes (H1 and H2) of the elements to the bottom plane (Sx-Sx′) ranges between 0.5° and 1.5° in the direction in which the difference (q−p) between the distance (q) from the intersection (Q) of the optical axis and the bottom plane (Sx-Sx′) up to the base edges (x,x, . . . ) shared by the elements and the distance (p) from the intersection (P) of the vertical line and the bottom plane (Sx-Sx′) up to the base edges (x,x, . . . ) shared by the element pair becomes plus (+) or minus (−).