Abstract text

A movable table unit provided here has a simple structure but can increase the precision of detecting the displacement of a movable table, and comprises a ring-shaped stationary base 1, a movable table 2 disposed inside the stationary base, spring members 3a to 3d interposed between the movable table and the stationary base, and a piezoelectric element 4 fixed to either the stationary base 1 or the movable table 2 and capable of expanding/contracting in the axis direction to exert either an expansion or contraction force on the other, to allow the movable table 2 to move relative to the stationary base 1. A strain gauge 8 is mounted in a strain occurrence site where strain occurs as the movable table 2 moves, so that the amount of travel of the movable table 2 is detected on the basis of the value detected by the strain gauge 8