A ball screw device includes a screw engaged into a nut member for forming two or more endless ball guiding passages and for receiving a number of ball bearing members, the nut member includes two or more conduits and recesses communicative with the helical grooves of the nut member, two deflecting devices are attached to end portions of the nut member and each include an inner member attached to the nut member and having two or more pathways aligned with the recesses of the nut member, and an outer member attached to the inner member and coupled to the inner member with one or more radially extended protrusions for suitably guiding ball bearing members.