To provide a fastener capable of more quickly performing operations than ever before, by highly accurately and easily performing the operations such as positioning, fixation and separation of two members to be fastened.

The fastener 10 is constituted so that a pressing ring 38 and a compression coil spring 40 forming a tapered pressing surface 42 (42a and 42b) on an outer peripheral surface for changing in a taper angle in the middle, are arranged in a circular recess 30 arranged on a fastening pin 12; a steel ball 36 is arranged in a circular through-hole 34 arranged in a peripheral wall part of the circular recess 30; the pressing ring 38 is pushed down by screwing a clamp bolt 44 in a screw hole 32; the steel ball 36 is pressed by a tapered pressing surface 42, and is protruded from the outer peripheral surface of the fastening pin 12; and the fastening pin 12 and a fastening bush 14 are fastened by engaging with an inside protrusion 60 of the fastening bush 14.