PURPOSE: To enable a tailstock to generate fixed force pressing the center even for both different length of a work and its thermal expansion, by controlling a driving gear so that a preset value may be obtained in a difference between thrust forces generated in each of the first and the second thrust force applying means of a thrust bearing in a main unit of the tailstock.

CONSTITUTION: A work mounting instruction is given to a feed control device 63, and if a tailstock main unit 32 advances, a center 50, engaging with a center hole Wa, tends to be pressed to a work W, and repulsive force of the center 50 generates a pressure difference between bearing pockets 44, 45. If this pressure difference becomes a value within a range set by a setter circuit 62, a comparator 61, stopping its minus signal having been fed to the feed control device 63 up to this time, causes a servomotor 35 to stop. In this way, fixed force pressing the center can be given to the work W even if it is formed in a different length. While if the work W and a rotary shaft 39 are thermally expanded during machining, the pressure difference increases by the repulsive force from the work, and a tailstock retreats by a plus signal if the pressure difference exceeds the preset range while holds the pressing force by stopping the motor 35 if the pressure difference becomes the preset value.