A needle assembly (1) includes a cover (5)(7) provided to be movable to a first position where a cannula (2)(3) is exposed and a second position where a distal end projects further than the cannula.In the cover, circumferential-direction locking sections (25)(43) or front-back-direction grooves (24)(42) continuing to the circumferential-direction locking sections or engaging protrusions (5a)(33a) movable along the circumferential-direction locking sections and the front-back-direction grooves are provided.
