Abstract: A seatbelt-adjusting device includes a belt-holding piece that is mounted slidably on a frame unit, and that is slidable on the frame unit between front and rear positions. A positioning member has left and right end portions and a bridge portion interconnecting the left and right end portions. The left and right end portions of the positioning member are respectively pivoted to left and right sides of the frame unit so as to be pivotable between a first position, in which, the bridge portion of the positioning member is spaced apart from the belt-holding piece, and a second position, in which, the bridge portion of the positioning member abuts against the belt-holding piece when the belt-holding piece is disposed at the front position.