A radical-curable seal member for fuel cell 4 having a glass transition temperature of −40° C. or lower made from a crosslinked product of a radical-curable composition containing (A) (Meth)acrylic polymer having a (meth)acryloyl group at a molecular chain end, (B) Monofunctional (meth)acrylic monomer, (C) Polyfunctional (meth)acrylic monomer and (D) Radical polymerization initiator, wherein the radical-curable composition contains 20 to 90 weight parts of component (B), 1 to 10 weight parts of component (C), 0.01 to 10 weight parts of component (D) with respect to 100 weight parts of component (A), a weight ratio [(B)/(C)] of the component (B) with respect to the component (C) being 4 to 24, and a content [(C)/{(A)+(B)+(C)}] of the component (C) with respect to a total of 100 wt % of the component (A), the component (B), and the component (C) being 1 to 7 wt %.