To provide an IC card which has its both smoothed sides by securing a contact between a specific oversheet and a thin plate where an IC module is embedded and applying an electric field of frequency of a specific range to make only the treated film of the oversheet generate the heat to conduct its fusion.

One of both sides of a film made of the nonpolar polyethylene terephthalate resin or polybutylene terephthalate resin having a ≤0.1 dielectric power factor at a frequency of 1 kHz to 1 MHz is irradiated by the ultraviolet rays or undergoes a corona discharge treatment. Thus, an oversheet 1 is obtained. Then a contact is secured between the oversheet 1 and a thin plate where an IC module 2 is embedded, and an electric field of frequency of 1 to 300 MHz is applied to the oversheet 1 to make only the treated film of the oversheet 1 generate the heat to conduct its fusion. Thus, it is possible to easily produce an IC card with its thickness uniformed and both sides smoothed.