Patent ID: 7905157

Claim:
A ball screw unit, comprising: a screw shaft that has a screw groove and spline grooves; a ball screw nut that is screwed to the screw groove of the screw shaft via balls; a spline outer cylinder that is splined to the spline grooves of the screw shaft, and that guides linear motion of the screw shaft in an axial direction of the screw shaft; a housing that holds one end of the spline outer cylinder, and that has a screw shaft passing wall in which a through hole, through which the screw shaft passes, is formed; and a biasing member that is arranged at the other end of the spline outer cylinder, and that biases the spline outer cylinder toward the screw shaft passing wall, wherein a tapered recess is formed in one of one end face of the spline outer cylinder and a face of the screw shaft passing wall, which faces the spline outer cylinder, and a tapered projection, which is fitted in the tapered recess, is formed in the other of the one end face of the spline outer cylinder and the face of the screw shaft passing wall, which faces the spline outer cylinder, so that the spline outer cylinder is allowed to move with respect to the housing when a force that overcomes a biasing force of the biasing member is applied to the spline outer cylinder.