A slider includes lower flanges placed on left and right side edges of a lower wing plate. Each of the lower flanges includes a downwardly inclined surface portion which is placed on the shoulder-opening-side tip portion on a side of its upper surface and on an outer side in a width direction of the slider, and which downwardly inclines toward a shoulder and downwardly inclines toward the outer side in the width direction of the slider. According to this, in a slide fastener having the slider, even if a sliding operation of the slider is repeated in the slide fastener, it is possible to avoid defects that the lower flange of the slider comes into sliding contact with the fastener tape and the fastener tape is broken, and it is possible to extend the life of the fastener tape.