An outer cylinder 2 for a prefilled syringe is mountable a piercing member 6 which includes a piercing member body 60 having a piercing member side engaging portion 62 and a hollow needle 61 having a needle portion at both ends thereof and mounted to the piercing member body 60. The outer cylinder 2 for the prefilled syringe has an outer cylinder body 4 which has a distal part 41 having an opening 48 and an outer cylinder closure member 5 which seals the opening 48 of the distal part 41, accommodates a sealing member 10 through which the needle portion 61b of the hollow needle 61 is penetrable, and is mounted on the distal part 41 of the outer cylinder body 4. The outer cylinder closure member 5 has a piercing member mounting portion 50 on which the piercing member 6 is mountable and a regulation portion which regulates the separation and rotation of the outer cylinder closure member 5 mounted on the outer cylinder body 4. The outer cylinder closure member 5 further includes an outer cylinder closure member side engaging portion 53 which engages the piercing member side engaging portion 62 when the outer cylinder 2 is pressed into the piercing member 6 from the side of the outer cylinder closure member 5 and which regulates the separation of the piercing member 6 from the outer cylinder closure member 5, after the outer cylinder closure member side engaging portion engages the piercing member side engaging portion 62.
