and 33 that are fused together forming an internal space 30 a therebetween in which a plurality of balls 31 are disposed the balancer 30 according to the second embodiment of the present invention is similar to that of balancer 20 according to the first embodiment of the present invention except the structure of supports 34 of balancer 30 is different from that of the structure of the supports 24 of balancer 20 as illustrated in fig5 and 6 the supports 34 according to the second embodiment of the present invention protrude parallel to first and second walls 32 a and 32 b of a first housing 32 which are opposite each other and the supports 34 are disposed at regular intervals along the first and second walls 32 a and 32 b the first housing 32 further includes a third wall 32 c ends 22 d of the first housing 32 extend from an end of the first and second walls 32 a and 32 b similar to the supports 24 according to the first embodiment the supports 34 of the second embodiment have a length such that the supports 34 extend from the first housing 32 to contact the wall of the recess 15 the surfaces of the supports 34 thereby abut portions of the front member 12 hence the first and second walls 32 a and 32 b are further increased in strength and additionally function to guide the.