A slide fastener, wherein in the fastener chain openable and closable from both ends thereof, a box pin and the insert pin, which can join with or separate from each other, are provided at least on anend of the fastener chain; and a protrusion facing the insert pin and projecting from an opposing face is provided at a front end of the box pin; the protrusion has slopes inclined in a direction ofapproaching the insert pin on upper and lower sides of the protrusion; and the lower side of the protrusion makes contact with a diamond of the reverse opening slider, while the upper side of the protrusion can guide the insert pin smoothly when the pin is inserted.