caster (120), and the wheel (121), freely turning the wheel (121) axis It reduced the yoke portion for supporting a (122a), through holes (111b) cylindrical stem portion which is rotatably held in a frame (111) and (122b), provided at the upper end of the stem portion (122b) diameter and (122c), the flange portion protruding radially outwardly at the upper end of diameter portion (122c) and (122d), outer diameter greater than the diameter of the fitted possible inner diameter and the stem portion to a reduced diameter portion and a, and a ring body having an opening provided for introducing a reduced diameter portion in the ring and (123a) and. With the stem portion (122b) penetrates through hole (111b) from the lower, reduced diameter portion (122c) is disposed above the through hole (111b), the ring body in the reduced diameter portion (122c) (123a) is By ring body (123a) is engaged with the upper portion of the through hole (111b) together is fitted in elastically deformed, casters (120) are rotatably supported on the frame (111).キャスター(120)は、車輪(121)と、該車輪(121)を旋回自在に軸支するヨーク部(122a)と、フレーム(111)の貫通孔(111b)内に回動可能に保持される円柱状のステム部(122b)と、ステム部(122b)の上端に設けられた縮径部(122c)と、該縮径部(122c)の上端で径方向外方に張り出した鍔部(122d)と、縮径部に嵌着可能な内径及びステム部の径よりも大きい外径を有し、縮径部を環内に導入するための開口が設けられたリング体(123a)と、を備える。ステム部(122b)が貫通孔(111b)を下方から貫通した状態で、貫通孔(111b)の上方に縮径部(122c)が配置され、縮径部(122c)にリング体(123a)が弾性変形して嵌着されるとともにリング体(123a)が貫通孔(111b)の上部で係止されることにより、キャスター(120)がフレーム(111)に回動可能に支持される。
