A slide fastener slider, in which a pair of projecting portions are formed such that they project from shoulder mouth side end portions of a pair of flanges to a shoulder mouth side, the flanges being erected on both right and left sides of a lower plate. Each projecting portion is constituted of a stepped portion formed by extending from the shoulder mouth side end portion of each flange to the shoulder mouth side, and a downward slope formed from the stepped portion up to a top face of the lower plate. The pair of projecting portions allow an inclination of a leg portion of a fastener element to be returned to a substantially horizontal state, thereby preventing contact between a fastener tape and each flange to block breaking of threads in the fastener tape.