To provide an adjuster for a chin strap capable of improving utility, safety and productivity.

This adjuster is an adjuster 24 in which the interior of an external frame 13 is divided into two spaces 18 and 19 by a retaining member 14. An edge member 16 forming one divided space 19 is equipped with a cut part 25. A ring-shaped end part 26 of an adjustable band is engaged with the edge member 16 at the side having the cut part 25 of the adjuster 24 so as to movably insert the adjuster 24 into the adjustable band.