PURPOSE: To satisfy the communication of treating liquid into a swingable barrel without forming several holes communicated with the inside of the barrel, by providing such an arrangement that the axial one side edge of a barrel-peripheral opening is projected to a degree larger than the projecting degree of the other side edge.

CONSTITUTION: A swingable barrel 20 having a few holes 22 and a top opening 23, comprises a barrel periphery 21 made of insulative materials, nets 28 laid over the holes 22 and side plates 25 laid on both sides of the barrel periphery 21 and made of insulative materials. An electrode cord 27 including an electrode 27A is led into the inside of the barrel 20 through a hollow hole 24 in one of swingable shafts 26 disposed at the side plates 25. In this barrel 20, one sie edge 21A, in the direction of the swingable shaft 26, of the opening 23 in the barrel periphery 21 is projected to a degree larger than the projecting degree of the other side edge. With this arrangement, there is no need of the provision of several holes communicated with the inside of the barrel 20, the communication of treating liquid into the inside of the barrel may be satisfied.