When a roller cylinder of a top roller is installed, it may collide against an outer bearing and damage it. Since the roller cylinder is loosened, when drafting is executed at a high speed, the roller cylinder may vibrate, causing non-uniform drafting. A pre-loading spring 30 is installed between an inner bearing 20 and an outer bearing 21 and on the inner circumferential side. Due to the elastic force of the pressurizing spring 30, inner rings 20b and 21b of the bearings rotate integrally with a shaft 10. When the roller cylinder 12 is installed, if it collides against the outer bearing 21, the pre-loading spring 30 acts as a buffer to prevent damage to the bearings. O-rings 31 and 32 installed between outer rings 20a and 21a of the bearings 20 and 21 fill the gap to prevent the roller cylinder 12 from loosening. As a result, uniform drafting can be executed at a high speed.