The invention relates to a ball screw device in which a screw shaft and a nut member are screwed together through a number of balls. In such ball screw device, the inner surface of a cover plate contacting the end surface of a nut main body is formed with a projecting return piece adapted to fit in a recess cut in the inner peripheral surface of the nut main body, the return piece being formed with a scoop that detaches the balls from the ball rolling groove of the screw shaft, and a direction switching passageway for guiding the detached balls to the inlet of a ball return hole, such raised portion being bisected into a first piece formed integral with the cover plate and a second piece fixed to the first piece by a curved surface including the centerline of the direction switching passageway.
