A ball screw device (10) having: a threaded shaft (1); a nut (2); multiple first balls arranged so as to be able to rotate freely inside a helical raceway formed by a thread groove (11) in the threaded shaft and a thread groove in the nut; an inner ring raceway groove formed in the outer circumferential surface of one axial end (12) of the threaded shaft; an outer ring (41) having an outer ring raceway groove opposing the inner ring raceway groove; and multiple second balls arranged so as to be able to rotate freely between the inner ring raceway groove and the outer ring raceway groove. Rotation of the threaded shaft is converted to linear motion of the nut by means of the first balls rolling inside the helical raceway in a loaded state. The outer ring has rolling body insertion holes (44) running from the outer circumferential surface to the outer ring raceway groove, and covers (45) covering the rolling body insertion holes, and the inner surface of the covers is formed in a concaveshape that forms a portion of the outer ring raceway groove.