Linear motion device

摘要

A ball screw (1) as a linear motion device according to the invention has retaining pieces (21) each having two concave surfaces (23) facing adjacent ones of rolling elements (9) respectively. Each of the retaining pieces (21) is disposed between adjacent ones of the rolling elements (9). A carbonitrided layer containing residual austenite of 15-40% by volume is provided in the surface layer of each of the rolling elements (9).