PURPOSE: To enhance accuracy, by erecting a ball screw between a pair of supports having spherical washers assembled therein while mounting a crosshead inserted through the aforementioned supports in a state threaded with the ball screw.

CONSTITUTION: A base table 1 is formed so as to erect two supports 2a, 2b. In this cse, spherical washers 4 are fitted to the lower ends of the supports 2a, 2b piercing through the base table 1 and received by rings 5. In addition, a ball screw 8 is vertically provided between the supports 2a, 2b and the lower end thereof is connected to a servo motor 9. Further, a crosshead 10 is provided to the ball screw 8 so as to allow said screw to pierce through the crosshead 10 and supported by the supports 2a, 2b and moved up and down with the rotation of the ball screw 8 to apply load to said ball screw 8. By this constitution, the vertical degree of each support is held with good accuracy and an accurate display value can be displayed.