Rolling element spacer in rolling guide device

A rolling element spacer used in a rolling guide device in which a pair of members perform a relative continuous motion through an endlessly circulating ball row, interposed between balls mutually adjoining in an endless circulation passage, and circulating together with the balls, the spacer comprising:

• a pair of ball holding seats, each ball holding seat has a concave spherical face approximating a spherical face of the ball and that makes sliding contact with the ball;
• an annular dropout prevention portion formed around each ball holding seat and that protrudes in a ball arranging direction from an edge portion of the ball holding seat and does not contact the ball seated on the ball holding seat;
• and
• wherein the ball holding seat and the dropout prevention portion are integrally formed from a single synthetic resin.