PURPOSE: To improve thermally fusion-bonding strength of plastic by a simple operation by irradiating a fusion-bonding part of an oriented and fixed plastic film with UV rays, then bringing the fusion-bonded part into contact with melted resin, and integrally fusion-bonding both.

CONSTITUTION: A grip fusion-bonding part 1a of a bottle body 1 obtained by blow-molding a parison of PET is irradiated with UV rays from an excimer laser to be surface-treated. Then, the body is disposed in a mold for molding a grip, molten PET resin of 310°C is injected by an injection molding machine to mold a grip 2, and both are simultaneously integrally fusion-bonded. The laser to be used is a KrF laser for oscillating UV rays having a wavelength of 248mm, a pulse width of 30nsec, a photon energy of 5.0eV and an intensity of 1.7×106/cm2. Thus, fusion-bonding strength of the plastic is largely improved.