A slide fastener in which one of the fastener stringers is separable from a tape insertion path at one side of a body of each of sliders 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. The rear ends of the upper and lower flanges at the one side of the body of the upper slider in the width direction are positioned forward with respect to the rear end of the upper slider at a side of a rear mouth. It is therefore possible to prevent fastener elements from being damaged and easily separate one of the fastener stringers from the upper slider using a simple structure.