Abstract: In a fastener of a post-installation type which is embedded after a drilled hole is provided at concrete structure, a sleeve (2) and a plug (3) press-fitted to the sleeve are positioned by convexoconcave engagement between a projecting portion at an inner periphery of an expansion portion (6) and a recess groove (11) at a tip end of the plug (3) before installation, and therefore the separation therebetween is prevented. After installation, the projection portion at the inner periphery of the expansion portion (6) expanded is again engaged with the recess groove (12) of the tip end of the plug (3). By this positioning effect, the fastener performs an effect for preventing a loosening between the sleeve and the plug against the vibrations.