Provided is a roller screw capable of preventing rollers moving from an unloaded return path to a loaded roller rolling path from coming into collision with a scooping portion. The roller screw has: a screw shaft 1 having a spiral roller rolling surface la formed on an outer peripheral surface thereof; a nut 2 having a loaded roller rolling surface 2a formed in an inner peripheral surface thereof; a circulation member 3 having an unloaded return path connecting one end of the loaded roller rolling surface 2a of the nut 2 to an opposite end thereof; and a plurality of rollers 4 arranged in a loaded roller rolling path 6 and the unloaded return path. In the circulation member 3, as a scooping portion that juts toward the screw shaft 1 and provided for scooping the rollers 4 moving in the loaded roller rolling path 6 up into the unloaded return path, a pair of diagonal corresponding parts 14 is provided which are in contact with diagonal parts 4e of a rectangular side surface of each roller 4 and a width between which is gradually narrower as they are deeper in the unloaded return path in such a manner that a cross section of the unloaded return path is closer to a rectangle.