By providing a rib portion 40 having a constant height in the range from 50% to 120% of the height of the highest point of a split lens structure between a plurality of split lenses, even when roll forming is performed at a high speed, trapping of air bubbles can be inhibited, and resin flow can be promoted; therefore, an optical element 10 having a surface on which a lens shape is formed and having a special optical effect can be obtained with few structural defects and high productivity.