This needle support assembly (9) includes a needle hub (23), a needle tube (3) retained by the needle hub (23), a cap (7) that includes a cap elastic body (73) for engaging with the outer periphery of the needle hub (23) and is fixed to the needle hub (23) by the engagement between the needle hub (23) and the cap elastic body (73), and an engagement release mechanism (8) for releasing the engagement between the needle hub (23) and the cap elastic body (73). The engagement release mechanism (8) includes a cap detachment ring (81) which is provided so as to be able to slide on the outer periphery of the needle hub (23) and can be detached from the needle hub (23). When the needle hub (23) moves toward the distal end in relation to the cap (7), the cap detachment ring (81) intrudes between the needle hub (23) and the cap elastic body (73), and the engagement between the needle hub (23) and the cap elastic body (73) is released.
