To surely prevent a bridge of a complicated rod body which is apt to cause the bridge by forming a plurality of projections whose positions are deviated in different regions respectively in the outer circumferential width direction of a polygonal rotary drum.

A plurality of projections 7a, 7b are formed at prescribed intervals in different regions 6a, 6b respectively in the outer circumferential width direction of an octagonal drum 6. When the octagonal drum 6 is counterclockwise rotated by the rotation of a motor, a rod body which is horizontally in contact with the outer circumference of the octagonal drum and lowered is alternately swung as shown by an arrow by the projections 7a, 7b so as to break a bridge. It is effective when the rod body is a polygon and has a complicated shape such as a tapered shaft, and the phase velocity of the deviation can be arbitrarily set The rotation direction of the octagonal rotary drum is normally/reversely alternately and repeatedly changed so as to expand the effects. The rotary drum may be not only the octagonal but any polygonal.