Abstract: In a passive seat belt system for a motor vehicle, a slide shoe mounted on a runner is composed of at least a pair of blocks spaced from each other in the direction of movement of the runner, in order to overcome the problem of the varying clearance between the runner and the guide rail. As the runner is moved along the guide rail, the two blocks contact the guide rail at their central portions and, in the meantime, an intermediate portion of the slide shoe is non-engageable with the guide rail. The result is that the slide shoe can contact the guide rail at the same portions even when the posture of the runner is changed due to the change of the curvature of the guide rail and the change of the cross-section shape of the guide rail.