Abstract: A slide table has two parallel axial ball rolling grooves of Gothic arch-like cross section provided in each of the inclined surfaces of an outwardly opening trapezoidal groove and has axial through-bores providing ball passageways formed rearwardly of the ball rolling grooves. The track shaft has Gothic arch-like ball rolling grooves formed axially thereof and corresponding to the ball rolling grooves of the slide table. Each of the Gothic arch-like ball rolling grooves has a narrow escape groove provided in the bottom thereof. Each of the semicircular ball passageways has a narrow concave groove in the bottom thereof and is in the form of a recess. The retainer comprises a wire rod having a straight portion and semicircularly bent portions extending from the opposite ends of the straight portion. The semicircularly bent portions are engaged with the concave grooves of the side plates. The slide table is supported on the track shaft by four rows of balls which are in four-point contact.