PURPOSE: To achieve the positioning of a reciprocating table at a low cost and with excellent accuracy.

CONSTITUTION: A right end part of a shaft 53R is brought into contact with a left end part of a nut 51, and a flange 531R is formed at the left end part of the shaft 53R. An approximately hollow housing 54R is fitted to the lower surface of the table 10 so as to cover the flange 531R, a spring 55R which is preliminarily compressed to the prescribed length is stored in the space constituted by the housing 54R and the flange 531R to allow the housing and the flange to be repulsive to each other, and a hook 56R is provided on the lower surface of the table 10. The housing 54R energizes the flange 531R by the spring 55R with the hook 56R being the limit, and the energizing force is applied to the nut 51 from the left side. The constitution on the right side is symmetrical to that on the left side relative to the A-A' line.