A device (1) for automatic injection , the injection device (1) comprising:a container (5), an injection needle (6)a housing (9, 11, 68, 72, 93) intended to receive, at least partially, the container (5), the container (5) being movable relative to the housing (9, 11, 68, 72, 93) between an initial position, in which the needle (6) is contained within the housing (9, 11, 68, 72, 93), an insertion position, distally spaced relative to the initial position and in which the needle (6) is exposed over a predetermined length, and a final position in which the needle (6) is contained within the housing (9, 11, 68, 72, 93)； and,a collapsible chamber (26, 59, 79, 96)wherein, with the container (5) in the initial position, the proximal wall is spaced proximally from the seal element (27, 29a, 60, 76, 97) and the chamber (26, 59, 79, 96) is filled with a fluid, wherein, with the container (5) in the insertion position, the fluid is at least partially expelled from the chamber (26, 59, 79, 96) and the proximal wall is caused to engage the seal element (27, 29a, 60, 76, 97), and, wherein, with the proximal wall engaging the seal element (27, 29a, 60, 76, 97), the container (5) being caused to move from the insertion position to the final position.
