A prefilled syringe (1) of the present invention has a gasket (3) composed of a gasket body (6) and a plunger-mounting member (7). The plunger-mounting member (7) has a distal part (71), spiral ribs (74, 75) formed on an outer surface of the distal part (71), a flange part (72), and a plunger-mounting part formed on an inner surface of a hollow part. The gasket body (6) has a spiral screwing part (63) which screws the spiral ribs (74, 75) and an accommodation part (62) for accommodating a portion where the spiral ribs (74, 75) are formed. A plunger (4) has a mounting distal part (40). The plunger-mounting part has a spiral concave portion (79) and an engaging rib (76) disposed at a side distal from the spiral concave portion (79). The mounting distal part (40) of the plunger (4) has a spiral projected portion (42) capable of screwing the spiral concave portion (79) and an engaging portion (41) which engages the engaging rib (76) of the plunger-mounting member (7).
