A slider for a slide fastener with a stop mechanism, comprising: a slider body having upper and lower blades (11, 12) and a guide post for connecting front end portions of the upper and lower blades; a pull tab having a pull tab body and an axis; and a bent leaf spring member, wherein the upper blade includes a claw hole formed at a side of the rear mouth of the slider body, a first post portion standing up at a front side with respect to the claw hole, and a second post portion standing up at a rear side with respect to the first post portion, wherein the leaf spring member includes a substrate portion pushing the axis of the pull tab from an upper side, a stopper claw portion extending from a rear end portion of the substrate portion, and a tongue portion extending downward from the substrate portion, and the leaf spring member is fitted into the slider body such that the stopper claw portion is able to be inserted into or released from an element guide path of the slider body by rotation of the pull tab, a first window portion is opened in the tongue portion, and a second window portion is opened from the substrate portion to the stopper claw portion, wherein the leaf spring member includes a first restraining portion which is disposed at the tongue portion and configured to abut against the first post portion to restrain upward movement of the leaf spring member, and a second restraining portion which is disposed on the substrate portion at a side of the stopper claw portion with respect to the tongue portion, and configured to abut against the second post portion to restrain the upward movement of the leaf spring member, wherein lower opened edges (56a, 57a) of the first and second window portions (56, 57) are disposed at a position to be respectively spaced apart from the first and second post portions (11a, 11c), when the pull tab lies down backward at its inclined angle α of 0° or when the pull tab lies down forward at its inclined angle α of 180°, and when the pull tab is operated in a range of 0° < α < 180°, while the axis of the pull tab abuts against the upper surface of the upper blade 11, and wherein the lower opened edges (56a, 57a) of the first and second window portions (56, 57) are disposed as first and second restraining portions at positions which respectively abut against the bottom surface of the front end portion of the first post portion 11a and the bottom surface of the front end portion of the second post portion 11c when the pull tab 20 is pulled and thus the axis 22 of the pull tab 20 is spaced apart from the upper surface of the upper blade 11, characterized in that the pull tab is configured so that a center surface of the pull tab body in a thickness direction thereof is disposed flush with a center surface of the axis in a thickness direction thereof. a slider body having upper and lower blades (11, 12) and a guide post for connecting front end portions of the upper and lower blades; a pull tab having a pull tab body and an axis; and a bent leaf spring member, wherein the upper blade includes a claw hole formed at a side of the rear mouth of the slider body, a first post portion standing up at a front side with respect to the claw hole, and a second post portion standing up at a rear side with respect to the first post portion, wherein the leaf spring member includes a substrate portion pushing the axis of the pull tab from an upper side, a stopper claw portion extending from a rear end portion of the substrate portion, and a tongue portion extending downward from the substrate portion, and the leaf spring member is fitted into the slider body such that the stopper claw portion is able to be inserted into or released from an element guide path of the slider body by rotation of the pull tab, a first window portion is opened in the tongue portion, and a second window portion is opened from the substrate portion to the stopper claw portion, wherein the leaf spring member includes a first restraining portion which is disposed at the tongue portion and configured to abut against the first post portion to restrain upward movement of the leaf spring member, and a second restraining portion which is disposed on the substrate portion at a side of the stopper claw portion with respect to the tongue portion, and configured to abut against the second post portion to restrain the upward movement of the leaf spring member, wherein lower opened edges (56a, 57a) of the first and second window portions (56, 57) are disposed at a position to be respectively spaced apart from the first and second post portions (11a, 11c), when the pull tab lies down backward at its inclined angle α of 0° or when the pull tab lies down forward at its inclined angle α of 180°, and when the pull tab is operated in a range of 0° < α < 180°, while the axis of the pull tab abuts against the upper surface of the upper blade 11, and wherein the lower opened edges (56a, 57a) of the first and second window portions (56, 57) are disposed as first and second restraining portions at positions which respectively abut against the bottom surface of the front end portion of the first post portion 11a and the bottom surface of the front end portion of the second post portion 11c when the pull tab 20 is pulled and thus the axis 22 of the pull tab 20 is spaced apart from the upper surface of the upper blade 11, characterized in that the pull tab is configured so that a center surface of the pull tab body in a thickness direction thereof is disposed flush with a center surface of the axis in a thickness direction thereof.