A gasket configured so that a pusher having a male screw thread on the outer periphery of its tip is connected to the gasket through the male screw thread and so that the gasket slides within a syringe outer tube when the pusher is operated in the longitudinal direction. The gasket includes: a gasket body having a hollow section and a female screw thread in the inner peripheral section of the hollow section engaged by the male screw thread； and projections on the outer peripheral section of the gasket body extending circumferentially of the outer peripheral section and axially arranged in spaced relation to each other. When the gasket is not yet inserted into the syringe outer tube, a screw thread located in a portion on the inner side of and in direct proximity to the projection has a smaller height than a screw thread located in the remaining portion.
