A ball screw having: a screw shaft having a spiral ball rolling groove; a ball nut having a ball rolling groove corresponding to the ball rolling groove; and a large number of balls interposed between the ball rolling grooves so as to roll freely; wherein the ball rolling groove of at least one of the screw shaft and the ball nut is ground so that a maximum value component of a number of undulation peaks per lead in the ball rolling groove is not in a range of from 0.95 nm to 1.05 nm centered on an integral multiple nm of a number m of load balls per lead calculated by an expression:

##EQU1##

in which P is a distance between centers of the adjacent load balls disposed at substantially equal intervals in the ball rolling groove, d_m is a ball pitch circle diameter, and L is a lead.