PURPOSE: To perform conveniently heat fusion of a thermoplastic resin molded article by a method wherein a dispersion liq. prepd. by dispersing a particulate graphite in a polymer soln, is applied on a fusing part of the molded article and after it is dried, fusion is performed by irradiating a microwave.

CONSTITUTION: As a place on which a particulate graphite dispersion liq. is applied, when a molded article to be fused is thin, it is applied on the opposite side of the face to be adhered and after it is dried by heating it at a temp. where the molded article is not deformed, the face to be adhered is brought into contact with another molded article. In addition, when the face to be adhered is thick, after it is applied on the adhering face side and is dried, if necessary, a thin film with the same substance as a resin to be adhered is placed on the applied face and it is brought into contact with another molded article to be adhered. Then, it is irradiated with a microwave. In this case, the part to be adhered is pref. pressed.