To provide an adjuster capable of easily adjusting height position of a leg without a tool.

This adjuster is provided with a shaft part 3a having external thread 2 formed on an outer circumference surface on one end side thereof, a spindle 3 connected to another end of the shaft part with forming spherical shape of larger diameter than the axial part and composed of a polygon surface spherical part 3b having a section perpendicular to an axis line AL1 of the shaft part chamfered to form a polygon, a socket 5 engaged relatively tiltably with the spindle via polygon recess part 6 in which more than half of the polygon surface spherical part of the spindle can be embedded, and fall-off prevention cap 10 preventing falling off of the socket from the polygon surface spherical part while allowing relative tilting motion of the spindle and the socket at a time of being fitted on an outer circumference surface of the socket.