A slide fastener (10, 40, 50) including: fastener stringers where continuous-shaped fastener elements are attached to opposing side edge portions of a pair of left and right fastener tapes; at least one slider (21a, 21b) which is allowed to pass through the left and right element rows constructed with the fastener elements; a separable pin (31, 51) which is attached to one end portion of one element row of the left and right element rows; and a box pin (32, 32', 52) which is attached to one end portion of an other element row, wherein in the slider (21a, 21b), an upper blade and a lower blade are connected to front end portions of shoulder opening sides by a guide post, flange portions are disposed in left and right side edges of the upper blade and/or the lower blade (22, 23), and rear openings are provided to rear end portions of the upper and lower blades (22, 23), the separable pin (31, 51) has a projecting portion (31b, 51b) which is projected toward the box pin (32, 32', 52) in an end portion area on a side of the element row, being characterized in that a difference (interval A - maximum value B) between an interval A between inner surfaces of the left and right flange portions in the rear end portion of the slider (21a, 21b) and a maximum value B of a dimension of the separable pin (31, 51) in a tape width direction is set to satisfy a relationship of "(dimension C of a portion of the box pin (32, 32', 52) in the tape width direction corresponding to a portion of the separable pin (31, 51) having the maximum value B) < (interval A - maximum value B) < (element width D of the fastener element)", the maximum value B is set to be smaller than the element width D, and within the end portion area where the projecting portion (31b, 51b) of the separable pin (31, 51) is formed, a dimension E of the area in a tape length direction where the dimension of the separable pin (31, 51) in the tape width direction is larger than the difference between the interval A and the element width D (interval A - element width D) is set to satisfy a relationship of "(dimension E) > (length of one pitch of the fastener elements of the element row) × 3 - (dimension of a coupling head of the fastener element in the tape length direction) × 3". fastener stringers where continuous-shaped fastener elements are attached to opposing side edge portions of a pair of left and right fastener tapes; at least one slider (21a, 21b) which is allowed to pass through the left and right element rows constructed with the fastener elements; a separable pin (31, 51) which is attached to one end portion of one element row of the left and right element rows; and a box pin (32, 32', 52) which is attached to one end portion of an other element row, wherein in the slider (21a, 21b), an upper blade and a lower blade are connected to front end portions of shoulder opening sides by a guide post, flange portions are disposed in left and right side edges of the upper blade and/or the lower blade (22, 23), and rear openings are provided to rear end portions of the upper and lower blades (22, 23), the separable pin (31, 51) has a projecting portion (31b, 51b) which is projected toward the box pin (32, 32', 52) in an end portion area on a side of the element row, being characterized in that a difference (interval A - maximum value B) between an interval A between inner surfaces of the left and right flange portions in the rear end portion of the slider (21a, 21b) and a maximum value B of a dimension of the separable pin (31, 51) in a tape width direction is set to satisfy a relationship of "(dimension C of a portion of the box pin (32, 32', 52) in the tape width direction corresponding to a portion of the separable pin (31, 51) having the maximum value B) < (interval A - maximum value B) < (element width D of the fastener element)", the maximum value B is set to be smaller than the element width D, and within the end portion area where the projecting portion (31b, 51b) of the separable pin (31, 51) is formed, a dimension E of the area in a tape length direction where the dimension of the separable pin (31, 51) in the tape width direction is larger than the difference between the interval A and the element width D (interval A - element width D) is set to satisfy a relationship of "(dimension E) > (length of one pitch of the fastener elements of the element row) × 3 - (dimension of a coupling head of the fastener element in the tape length direction) × 3".