A ball screw device has: a screw shaft rotationally moving during use, a nut having a protruding non-rotating side engaging portion at an end portion on one side in an axial direction, the nut linearly moving during use, balls arranged between a shaft-side and nut-side grooves, and a driving member fixed to the screw shaft having an arc-shaped rotating-side engaging groove portion into which the non-rotating side engaging portion can be inserted in the axial direction, and which can be engaged with the non-rotating side engaging portion in a circumferential direction.