This thermosetting adhesive composition contains as a component (A) a vinyl compound in which a terminal end of a bifunctional polyphenylene ether oligomer is converted to a vinyl group, as a component (B) a maleimide resin, and as a component (C) a thermoplastic elastomer, the equivalent ratio of vinyl groups in the component (A) and maleimide groups in the component (B) being 1.0:0.5 to 1.0:4.0, the proportion of the component (C) in the total weight of the component (A), the component (B), and the component (C) being 55 to 95% by weight, the ratio of styrene units of the component (C) with respect to the total weight of the component (C) being 10 to 40% by weight, the tensile stress at 100% elongation being 0.1 to 2.9 MPa, and the elongation at break being 100% or greater.