A protective film (10) is eccentrically adhered to a concave-side transfer surface (3b) of a first mold (3) which is used in a plastic lens forming mold, and part (10a) of the peripheral portion of the protective film is projected laterally from the mold (3). The protective film (10) comprises a film layer with an outer diameter smaller than that of the first mold (3), and an adhesive layer with a relatively low adhesive strength which is formed on one surface of the film layer.