To provide a ball screw which has less limitation of the usage environment, and is easy to impose.

A ball screw 1 is comprised of a screw axis 12, a nut 13, through which the screw axis 12 is inserted, and a ball 14 which is provided between the nut 13 and the screw axis 12, and the ball 14 is held movably between an internal screw groove 17 and an external screw groove 18. First and second restricting means 21, 22 for restricting the moving range of the ball 14 along the external screw groove 11 and a feedback passage 23 for feeding back the ball 14, at an end side arranged along the external screw groove 18 into the other end side. Communication holes 51, 52 are formed near longitudinal holes 33, 34 which form the feedback passage 23, and a guide member 64 is pressed into the communication holes 51, 52. A shell part length L of the guide member is set to dimension, such that the top end is projected in the external screw groove 11, in a state of coming into contact with the step of the communication holes 51, 52 for the head part.