A planar coil element of the present invention includes an insulating base film having a first surface and a second surface opposite to the first surface, a first conductive pattern deposited on the first surface side of the insulating base film, and a first insulating layer covering the first conductive pattern on the first surface side, in which the first conductive pattern includes a core body and a widening layer deposited by plating on the outer surface of the core body, and the ratio of the average thickness of the first conductive pattern to the average circuit pitch of the first conductive pattern is ½ or more and 5 or less.