The invention relates to a resonant tag including an insulating thin film
and coiled circuits made of a metal foil respectively formed on both sides
of the insulating thin film. The coiled circuits are formed in an
electrically connected relation to each other with a space at the center
of the insulating thin film. Said both coils are almost superimposed on
each other to form a capacitor, thereby constituting an LC circuit. The
area of a portion of each side of the thin film, said portion being
surrounded by the innermost peripheries of both coils and having no metal
foil on both sides, is controlled to at least 16% based on the whole area
of said one side of the tag, whereby a resonant tag having an area of at
most 700 mm.sup.2 can be obtained.