Provided is a ball screw module including a screw shaft, a nut member, a ball connector, and a circulating device inside the nut member. The screw shaft and the nut member constitute a first load rolling groove. The circulating device, being connected with the first load rolling groove, has a first turning section and a second turning section, and includes a first guiding groove and a second guiding groove. The first guiding groove has a radius of curvature greater than that of the second guiding groove when the ball connector passes the first turning section. The first guiding groove has the radius of curvature smaller than that of the second guiding groove when the ball connector passes the second turning section.