An apparatus for supporting a worker's body part, for example a surgeon's arm, is provided. The body part is supported by a base movably supported by a support. The apparatus has a free mode and a limitation mode, which are switchable. When it is determined that the body part is attempting to move the base or a fastening member, the operating mode is switched to the free mode. When it is determined that the body part is not attempting to move the base or the fastening member, the operating mode is switched to the limitation mode. The free mode allows the fastening member to fasten the body part on the base and allows a brake to release limitations to the motions of the base. The limitation mode allows the fastening member to release the body part from being fastened and allows the brake to limit the motions of the base.