Linear bearing apparatus

A linear bearing apparatus which comprises:

• a first guide rail fitted to a first physical body to extend lengthwise thereof and a second guide rail fixed to a second physical body to extend lengthwise thereof, said second physical body being moved toward either sense of the prescribed direction relative to the first physical body;
• a retainer assembly which is disposed between the first and second guide rails, and is formed of a plurality of rolling elements and a retainer for supporting said rolling elements, and, where the second physical body is moved relative to the first physical body for a certain distance, is moved relative to the first physical body for substantially half said distance toward the same sense toward which the second physical body is carried;
• and
• urging means for imparting an elastic force to the retainer assembly to prevent said retainer assembly from progressively drifting when the second physical body repeatedly moves relative to the first physical body toward either sense of a direction alternately.