A rolling element screw device is provided with a power transmission mechanism for moving a retainer ring 14 in an axial direction in accordance with lead angles of spiral grooves 11a, 12a while rotating the retainer ring 14 in a condition of maintaining a constant relationship with respect to a rotational phase of a rotating side member in accordance with the rotation of the rotating side member. The power transmission mechanism is provided with an external tooth 17 formed to a screw member 11, an internal tooth 18 formed to a nut member 12 and a plurality of planetary gears 19 held to be rotatable to circumferentially predetermined positions of the retainer ring 14 in a condition meshed with the external tooth 17 and the internal tooth 18, respectively, the external tooth 17 is formed so as not to overlap with the screw side spiral groove 11a formed to the screw member 11, and the internal tooth 18 is formed so as not to overlap with the nut side spiral groove 12a formed to the nut member 12. According to such structure, there can be provided a rolling element screw device capable of maintaining always constant the moving amount in both the axial directions of the retainer ring.