Provided are an antenna circuit constituent body for an IC card/tag capable of reducing environmental load in a manufacturing process for joining both end portions of an antenna circuit pattern layer and capable of enhancing reliability of joined portions of the both end portions of the antenna circuit pattern layer: and a method for manufacturing the antenna circuit constituent body for an IC card/tag. In the antenna circuit constituent body for an IC card/tag, an insulating layer (107) is formed so as to extend from an upper part of a first circuit pattern layer part (103), via an upper part of a third circuit pattern layer part (101), and to an upper part of a second circuit pattern layer part (104). A conductive layer (108) is formed on the insulating layer (107) so as to bring the first circuit pattern layer part (103) and the second circuit pattern layer part (104) into conduction. The insulating layer (107) has a plurality of inclined end surfaces on each of the first circuit pattern layer part (103) and the second circuit pattern layer part (104).