To eliminate a malfunction associated with operation torque fluctuations by reducing the operation torque fluctuations.

A ball screw 10 is supported such that both ends thereof can be freely rotated and can not be moved in the shaft direction by a support unit 50 while a screw shaft 11 is arranged in the horizontal direction. A nut 12 is fixed to a movement table 51 being a counter member while a ball return path and end deflectors 16, 18 are located on the above part of the nut 12. The screw shaft 11 is disposed such that the end part thereof is connected to an output shaft of a motor 52, and is rotated by the motor 52. The movement table 51 which is fixed to the nut 12 by rotation of the screw shaft 11 and is guided by a linear motion guide device 53 is moved along the longitudinal direction of the screw shaft 11.