PURPOSE: To simplify constitution, to reduce size, and to perform excellent absorption of rotation vibration of a screw shaft.

CONSTITUTION: In a ball nut 5 comprising a nut part 2 joined in a screwed-in state with a ball screw 1; and a mounting part arranged at the outside 4 of the nut part 2 and mounting a transfer object 3 on the nut part 2, a plurality of plate-form resilient members 6 are arranged between the nut part 2 and the mounting part 4. The resilient member 6 is integrally formed at the nut part 2 and the mounting part 4, one end is connected to the nut part 2 and the other end to the mounting part 4. A shape is deformed only in a plane vertical to the axis CL of the nut part 2 and extended approximately along the outer periphery of the nut part. The resilient member is arranged face- symmetically to a surface containing the axis CL of the nut part 2 in a vertical surface and the nut part 2 and the mounting part 4 perform relative translation in a vertical surface.