A method of manufacturing an electronic device includes: roughening an underside surface of a film made of a resin, opposite to a mounting surface of the film for mounting a circuit chip; forming a conductor pattern on the mounting surface of the film, thereby obtaining a substrate made of the film where the conductor pattern is formed; and attaching a thermoset adhesive to a conductor-pattern-formed surface of the substrate. The method further includes: mounting the circuit chip to be connected to the conductor pattern on the substrate via the thermoset adhesive; clamping the substrate by a heating apparatus having a presser section and a support section, the presser section abutting the circuit chip mounted on the substrate and the support section abutting the underside surface of the roughened film; and fixing the circuit chip to the conductor pattern by heating and hardening the thermoset adhesive using the heating apparatus.