PURPOSE: To contrive reliable prevention in generation of creases in a decorated molded product while maintaining productivity, by a method wherein a pair of crease preventive guide bars which are rotated while placing a film between them and applies tension to the film are fitted to a downstream side of a film transfer direction of a molding tool.

CONSTITUTION: A film 2 is positioned by a positioning sensor 8 to send a fresh pitch of a patterned part into a position facing on a cavity 1a of a female mold 1 while turning a winding roll 4, and when a fresh pattern comes to the position facing on the cavity 1a, the winding roll 4 is suspended. Then a rotary member 10 is turned by a fixed angle in the direction of an arrow, a pair of crease preventive guide bars pinch the film 2 and apply tension to the same, through which the creases extending to the upper part from the lower part of the film 2 are smoothed. Then a heating block 7 is moved to a position facing on the cavity 1a, the heating block 7 is brought into contact with the film 2 of a cavity 1a surface under this state, the film 2 is heated with the heating block 7 and resin is injected within the cavity 1a by joining a female mold 1 and male mold 20 to each other.