To easily realize extremely various using styles by detachably assembling an attracting magnet in a supporting plate, and turning over both the sides of the above plate to fix the supporting plate to a mouthpiece.

A magnet 21 is inserted in one of attaching holes 12, 12,... with an attracting face made to correspond to the back side of a supporting plate 10 and detachably attached to the supporting plate 10 by fastening a set screw 12b. In this case, set screws 12b, 12b are screwed in the tapped holes 12a of other attaching holes 12, 12. In addition, the height of the magnet 21 is set up so as to be slightly larger than the thickness of the supporting plate 10. The supporting plate 10 selects either of a surface side and a back side as the attracting face by turning over the magnet 21, and is fixed to a mouthpiece.