There is provided a slide fastener in which one of the fastener stringers is separated from a tape insertion path at one side of a body in the width direction when a lateral pulling force directed outward in the width direction of the fastener tapes is applied to a pair of fastener stringers. At least one opposing surfaces of an upper and lower flange at one side of the body in the width direction has a protrusion on the rear end portion thereof, and the opposing surfaces of the upper and lower flanges at one side of the body in the width direction respectively have straight portions which are parallel with each other except for the position at which the protrusion is formed.