Patent ID: 8584546

Claim:
A ball screw mechanism, comprising: a ball screw shaft having a first ball screw groove engraved on an outer circumferential surface thereof; a nut member formed in a cylindrical shape and having a second ball screw groove on an inner circumferential surface thereof, the nut member being disposed on an outer circumferential side of the ball screw shaft, and being screw-engaged with respect to the ball screw shaft via balls which are installed between the second ball screw groove and the first ball screw groove; and one circulation member connected to both ends of the nut member along an axial direction thereof, which circulates the balls through a circulation passage provided on an exterior of the nut member from one end side in a displacement direction of the nut member to the another end side thereof, wherein the circulation member includes two main body parts each fixed to a respective end surface of the nut member without covering an entirety of the respective end surface, each of the main body parts including an uncovered outermost end in the axial direction, and includes a cylindrical part connected to the main body part, and the circulation member includes the main body parts installed on a pair of mounting portions each of which is cut out in a three-sided shape on an outer circumferential surface of each of the ends of the nut member and each of which extends to a respective outermost axial end of the nut member, the cylindrical part is disposed on an outer circumferential side of the nut member, and a portion of the circulation passage is formed in the interior of the cylindrical part.