To obtain a desired shape without spending much time for fabricating fine grooves by forming helical groove on the surface of a roll.

Fine grooves are formed, in a single strip or multistrip helical shape, on the surface of a patterned roll 1 and the helical angle is set depending upon the use applications of an optical sheet and the groove is of a V or U-shaped. The matrix of the patterned roll 1 is tool steel with a specified outside dia. and a specified length shaped like a roll. In addition, the surface of the patterned roll 1 is plated with a hard copper, for example, which is somewhat less durable than a non-electrolytic nickel-plated face but reduces the wear of a cutting tool. After cutting the surface, it is treated by plating a non-electrolytic nickel as a protecting film to a specified thickness, on the cut surface, so that the surface hardness and the durability are adequately secured without collapsing the groove shape. Thus a continuous cutting fabrication process can be employed by forming the groove helically and the switching of cutting, rough and finish fabrications for every working pitch and the tool replacement are dispensed with. Consequently, the groove can be fabricated in the continuous cutting mode and also the edge wear of the cutting tool can be reduced and further, the manufacturing time can be shortened significantly.