PURPOSE: To obtain excellent adhesive properties of a resin film and an excellent external appearance by embossing the film and forming a linear air bleeding groove on a contact surface with a preformed form.

CONSTITUTION: A preformed form 4 is injected from a die 3 between molds 1 and 2. A decorating resin film 5 is previously placed on the inner surface 2A of the mold 2. Then, the molds 1, 2 are closed, the air is blown in the form 4 by gas blowing means to be blow-molded. The film 5 provided with means for air bleeding in the form 4 is provided. That is, protruding stripes 12 are formed by embossing, and linear air bleeding grooves 13 are formed on the preformed form contact surface 11A of the film 11. A through hole 6 for efficiently exhausting the air out of the molds is provided at the lower surface side of the mold 2.