To form cut grooves to a plastic molded object comprising a thermoplastic resin by a press plate in which diamond cut grooves are carved for simplifying a process and forming a metal vapor deposition film to the plastic molded object and to eliminate a problem of the cracking of the vapor deposition film at this time.

In a method for forming a company mark or the like to a plastic molded object, a thermoplastic molded object 1 having a softening point within a temp. region of 80-150°C, a transfer film wherein the metal vapor deposition layer is formed on a plastic base material layer having stretchability through a release layer and an adhesive layer is arranged on the vapor deposition layer and a press plate 3 having diamond cut grooves provided on the surface thereof and provided with heating elements are provided and the heated press plate 3 is pressed to the part 1a where a company mark is formed of the plastic molded object 1 through the transfer film 2 to form the metal vapor deposition film layer having the company mark developed thereon.