The present invention is characterized by being provided with: a rotary wheel 1 which has an opening 10 formed on the front-face side, a wall surface portion 15 formed on the back-face side, and a through-hole 13 formed in the wall surface portion 15； a bearing holder 2 that is inserted in the through-hole 13 from behind； a bearing 3 that is mounted to the bearing holder 2； a cap member 4 that is coupled to the bearing holder 2 from the front face side so as to fix the bearing holder 2 to the wall surface portion 15 of the rotary wheel 1； and a shaft member 5 that is mounted to a stand 100, wherein a shaft 52 formed in the shaft member 5 is pressed into the bearing 3 so as to be joined together.
