A method for manufacturing a rod with an optical thin film which comprises forming a rod block by arranging a plurality of rods each having a circular cross section in parallel to one another along the axis of each rod and by allowing a resin to enter gaps between rods adjacent to one another to fix the rods to one another. The rod block is cut into a predetermined length. The endfaces of each rod positioned on the cut endface of the rod block are then polished. An optical thin film is formed on the polished endfaces of each rod. The resin has a melting point higher than the temperature used in forming the film. The rods are separated from one another by removing the resin from the rod block.