To adjust the gap of a sash at an arbitrary position and fix it by movably constituting a gap lock body and a crescent receiver and processing contact faces thereof to have a rugged face such as a saw-toothed shape.

A gap lock body 1 and a crescent receiver 2 are made mutually movable and the contact faces of the gap lock body 1 and the crescent receiver 2 are processed to have a saw-toothed shape. And the crescent receiver 2 is formed to be fixable at an arbitrary position within the range of an aperture 4 provided in the gap lock body 1. A fastening hardware 5 is attached to the crescent receiver 2 to draw the crescent receiver 2 close to the hardware when the crescent lock of the sash is locked and further, push the fastening hardware 5 by the crescent lock and bring the crescent receiver 2 and the gap lock body 1 into close contact and securely fix them. In this way, the gap of the sash can be adjusted at an arbitrary position and fixed.