A roller screw includes: a screw shaft 1 having an outer peripheral surface in which a spiral roller rolling groove 1a is formed; a nut member 2 having an inner peripheral surface in which a spiral loaded roller rolling groove 2a is formed so as to oppose to the roller rolling groove 1a; a return pipe 4 connecting one and another ends of a loaded roller rolling groove 2a of the nut member 2; and a plurality of rollers 6 disposed in the loaded roller rolling passage 3 and the return pipe 4. A spacer 31 is disposed between a pair of adjacent rollers 6, 6 so as to prevent the paired rollers 6, 6 from contacting each other. According to such roller screw, the rollers can be smoothly circulated without causing any skew.