Free ball bearing, support table, carrying equipment, and turntable

A bearing unit comprising:

• a ball retainer having a semispherical recessed surface;
• a plurality of retainer balls disposed on the semispherical recessed surface, the plurality of retainer balls having a same diameter R1;
• a main ball rotatably supported by the plurality of retainer balls and having a diameter R2 larger than the diameter R1;
• a housing that has a shape surrounding the ball retainer, has a circular opening smaller than the diameter R2, and is disposed such that a portion of the main ball protrudes toward a tip end from a base end through the opening;
• a retainer ball-pressing ring disposed in the housing;
• and
• a ring moving mechanism that is connected with the retainer ball-pressing ring, wherein:
• the retainer ball-pressing ring includes a substantially cylindrical pressing member inserted in an internal space between the semispherical recessed surface and the main ball toward the base end;
• the retainer ball-pressing ring is moved by the ring moving mechanism from a pressing position to a standby position along an unit center axis that extends along the protrusion direction of the main ball and passes through a center of the main ball;
• when the retainer ball-pressing ring is at the pressing position, the pressing member restricts or prevents rotation of the plurality of retainer balls by pressing the plurality of retainer balls;
• and
• when the retainer ball-pressing ring is at the standby position, the plurality of retainer balls of which the rotation is restrained or prevented by the pressing member is released.