An adjuster with a frame attachable to the front end portion of an instrument tailpiece, a lever member with a base portion and a front plate portion swingably supported by the frame, a mounting portion with an adjusting screw positioned therein, an anchoring portion extending from the lever member that projects through an anchor hole to the surface side of the tailpiece to removably anchor a string of the instrument, and a swing transmitting member provided to the frame so as to be interposed between the adjusting screw and the lever member. The swing transmitting member is swingably supported by the frame and includes one or more transmitting levers extending along the string. When the adjusting screw is screwed into the mounting portion, one end of the transmitting lever is pushed down and another end pushes up the lever member, and the anchoring portion is swung to stretch the string.