A gasket (3) of a prefilled syringe (1) is composed of a gasket body (6) and a plunger-mounting member (7). The gasket body (6) has a plunger-mounting member removal prevention rib (62) formed on an inner surface thereof. The plunger-mounting member (7) has an outer projected part (73) which engages the plunger-mounting member removal prevention rib (62) of the gasket body (6), a plurality of elastically deformable inner projected parts (75) which are extended obliquely from an inner portion of a proximal side of the plunger-mounting member (7) toward a central and distal end thereof, and plunger removal prevention locking parts (76) formed at free ends of the inner projected parts (75) respectively. The plunger (4) has a distal end part (42) capable of entering the plunger-mounting member (7) and an outer projection part (43) which engages the plunger removal prevention locking parts (76) of the plunger-mounting member (7).
