To insert a ring terminal into a fusible link block so as to position surely.

A turn back prevention member 12 is hanging down from the inner wall face 3b of a protection cover 3 in the vicinity of an opening portion, and turns in the insertion direction of a wire with ring terminal via a hinge, and the retreat of the wire with ring terminal after insertion is blocked by a turn back prevention member 12 so as to position the ring terminal and a connection portion. The turn back prevention member 12 has a right-angled triangle-like cross section, a turn back prevention portion 12a is hanging on the inner wall face 3b of the protection cover 3 for blocking the retreat of the ring terminal, an introduction portion 12b, which turns in the insertion direction of the ring terminal, is linking formed slanting upward from the tip of the return back prevention portion 12b, and a stopper portion 12d, which prevents turning in anti-insertion direction via hinge 12c on an inner wall face, is integrally molded at one end of the introduction portion 12b.