<p>Intended is to provide a roller screw, which is freed from any undercut even if a circulating pipe having a twisted roller return passage of a rectangular section is halved. In order to circulate a roller, there are provided a direction turning passage constituting part (9) and a circulating pipe (8). A direction turning passage is formed in the direction turning passage constituting part (9), and a roller returning passage (11) is formed in the circulating pipe (8). This circulating pipe (8) is constituted by jointing a pair of split pieces (18a and 18b), which are halved along the apexes (11a and 11b) of the diagonal lines of the roller returning passage (11) having a section shaped rectangular and twisted.</p>
