In an adjustment device for a frictional force adjustment portion in a section, an inner circumferential portion of the section includes: a support hole formed from rolling bearings at both ends; a frictional force generation portion configured of a brake shoe, a coil spring, and a hexagon socket set screw and generates a frictional force against a rotary shaft inserted into the support hole; and a frictional force adjustment portion configured of the hexagon socket set screw and adjusts the frictional force in the frictional force generation portion. The adjustment member driving actuator adjusts the frictional force of the frictional force adjustment portion by rotating normally and reversely the adjustment member such that the frictional force in the frictional force generation portion of the section falls within a predetermined range.