A slider for a slide fastener includes a stopper mechanism formed for “forward use,” in which the surface where coiled fastener elements are attached on a fastener tape is the front surface, can be used for “reverse use,” in which the surface where the coiled fastener elements are attached on the fastener tape is the back surface. The inner surface of the lower blade of the slider body of a slider has a protrusion that extends in the forward-reverse direction from a guiding bar towards a posterior opening. The protrusion has a first horizontal upper surface on the guide bar end of the protrusion that is highest and a second upper surface on the posterior opening end that is lower than the first upper surface.