Antenna circuit constituent body for IC card/tag and IC card

An antenna circuit constituent body for an IC card/tag, comprising:

• a base material made of a resin film;
• a first circuit pattern layer formed on one of surfaces of the base material and made of an electrically conductive body including metal as a main component;
• and
• a second circuit pattern layer formed on the other of the surfaces of the base material and made of an electrically conductive body including metal as a main component, wherein
• at least either of the first circuit pattern layer and the second circuit pattern layer includes a coiled pattern layer,
• a part of the first circuit pattern layer;
• a part of the second circuit pattern layer, the part of the second circuit pattern layer facing the part of the first circuit pattern layer with the base material interposed;
• and a part of the base material, the part of the base material interposed between the parts of the first circuit pattern layer and the second circuit pattern layer constitute a capacitor,
• the first circuit pattern layer and the second circuit pattern layer are electrically connected so as to allow electrical continuity therebetween, and
• the base material includes a plurality of void-state-air layers, a relative density of the base material with respect to a density of the resin is less than or equal to 0.9, an average volume of the void-state-air layers is greater than or equal to 2 μm3 and less than or equal to 90 μm3.