A reverse opening slide fastener in which upper and lower sliders (50, 60) are arranged having rear openings mutually opposed and in which the top end of an insert pin can be inserted beyond a rear opening side tip of a guide column of a lower slider when the insert pin is inserted into the upper and lower sliders (50, 60) from a shoulder opening of the upper slider, including: a right-and-left pair of first and second fastener stringers (16, 17); the insert pin and a box pin which are arranged respectively at a lower end of inner side edge sections of the first and second fastener stringers (16, 17); and the upper slider and the lower slider which open and close the first and second fastener stringers (16, 17); wherein the insert pin includes a side edge at the box pin side and a side edge at a tape inner side being arranged opposite to the side edge at the box pin side; a first sloped section sloped in a direction to be apart from the box pin toward the top end of the insert pin is formed at the side edge at the box pin side; and the first sloped section is formed as being intersected, at an intersection point, with an extension line obtained by extending a planar section of the side edge at a tape inner side to the top end side of the insert pin and has a shape sloped at an angle to be contacted to the guide column of the lower slider or to be apart from the guide column when the insert pin is inserted to the upper and lower sliders (50, 60), characterized in that the insert pin is structured so that in a state that the side edge at a tape inner side is slidingly contacted to a flange of the upper slider and the side edge at the box pin side is slidingly contacted to an opposing side edge of the box pin, a distance between a contact point of the side edge at the box pin side with the box pin and the intersection point is larger than a distance between the contact point and a tip of the guide column. a right-and-left pair of first and second fastener stringers (16, 17); the insert pin and a box pin which are arranged respectively at a lower end of inner side edge sections of the first and second fastener stringers (16, 17); and the upper slider and the lower slider which open and close the first and second fastener stringers (16, 17); wherein the insert pin includes a side edge at the box pin side and a side edge at a tape inner side being arranged opposite to the side edge at the box pin side; a first sloped section sloped in a direction to be apart from the box pin toward the top end of the insert pin is formed at the side edge at the box pin side; and the first sloped section is formed as being intersected, at an intersection point, with an extension line obtained by extending a planar section of the side edge at a tape inner side to the top end side of the insert pin and has a shape sloped at an angle to be contacted to the guide column of the lower slider or to be apart from the guide column when the insert pin is inserted to the upper and lower sliders (50, 60), characterized in that the insert pin is structured so that in a state that the side edge at a tape inner side is slidingly contacted to a flange of the upper slider and the side edge at the box pin side is slidingly contacted to an opposing side edge of the box pin, a distance between a contact point of the side edge at the box pin side with the box pin and the intersection point is larger than a distance between the contact point and a tip of the guide column.