To improve the work efficiency by forming a fastener into one body beforehand to enable a fastening work, enlarge the thickness range of a plate of a member to be fastened, and improve fastening strength.

A fastener body 1 has a diameter such that the body 1 can be inserted into a mount hole 5a of a member 5 to be fastened has a large diameter portion 1a having at its top end an outwardly extending flange 1d adapted to contact the surface of the member 5 and a taper portion 1c which connects coaxially the portion 1a with a small diameter portion 1b. An elastic lock member 3 having a diameter such that the member 3 can be inserted into the hole 5a and a slider 2 are fitted onto the portion 1b successively from below, and a fastening screw rod 4 passing through a center hole 1e of the body 1 and a bottom wall 1f is screwed into a threaded hole 2d provided at the bottom wall 2a of the slider 2 to form them into a single body. The single body is inserted from outside into the hole 5a and the rod 4 is turned from outside by means of a tool so that the slider 2 is moved through thread to push up the member 3 so as to expand the diameter thereof, whereby the member 3 is pressed against the rear side of the member 5 to be fastened.