A roller screw of the present invention has a screw shaft 1 having a roller rolling surface 1a spirally formed with a lead on an outer surface thereof; a nut 2 having a roller rolling surface 2a spirally formed on an inner surface thereof to face the roller rolling surface 1a of the screw shaft 1; and a plurality of rollers 4 arranged in a rolling path 3 between the roller rolling surface 1a of the screw shaft 1 and the roller rolling surface 2a of the nut 2 and moving around the screw shaft while rotating on rotation axes of the rollers. In this roller screw, each of the rotation axes 4a of the rollers 4 substantially crosses a center line 1b of the screw shaft 1. Since each of the rotation axes 4a of the rollers 4 crosses the center line 1b of the screw shaft 1 (in other words, the rollers 4 arranged in the rolling path 3 are not skewed from the beginning) even when the rolling path 3 has the lead, the roller 4 are allowed to move smoothly.