The present invention provides rolling element spacers used in a rolling guide unit provided with an endless circulating passage for balls; arranged with plural balls alternately therewith in the endless circulating passage; and circulated with these balls in the endless circulating passage. Each of the rolling element spacers has a pair of retaining seats which the balls contact, and is formed so that, on a ball cutting plane perpendicular to the center of rotation of each ball, each retaining seat and a relative ball contact each other at only the two portions of the retaining seat that are in the vicinity of both ends thereof.