When a slide piece is fitted to a slide groove, the slide piece can be slid. When a latch is caught by recesses, a position of the slide piece in the slide groove is stabilized. Since the slide groove is provided with a plurality of the recesses at constant intervals, among the recesses, the recess at a most suitable position is selected and the latch is caught by the recess. The slide piece is integral with the inserting portion of a strap and therefore, the position of the slide piece is determined so as to adjust a length of the strap around the wrist. Further, the latch is only urged by a spring and the recess is not so deep as to engage the latch and therefore, when the slide piece is pushed or pulled by exerting force, the position of the slide piece can also be changed.