To prevent separation of first and second engagement members of a fixing device from structural materials during fixing work of a pair of structural materials.

An abutting member 2 is provided with a first blocking plate pat 2g and a second blocking plate part (not shown). Thicknesses of the first blocking plate part 2g and the second blocking plate part substantially match a distance between connection parts 4f, 4f of first engagement parts 4b, 4b and a distance between connection parts of second engagement parts (not shown) when the first and second engagement members 4, 4' are positioned in engagement positions. A tip 2i of the first blocking plate part 2g is positioned in an engagement groove A1 of one structural material A, and it is inserted between the connection parts 4f, 4f of the first engagement parts 4b, 4b. A tip of the second engagement part is positioned in an engagement groove of another structural material (not shown), and it is inserted between the connection parts of the second engagement parts.