The needle assembly (10A) includes a needle protection member (16) and a rotor (20). The rotor (20) has a rotor body (74) and a restriction portion (78). When the needle protection member (16) in the initial state is displaced from the protection position to the use position and returns to the protection position, the restriction portion (78) is displaced from the initial position to the lock position by the rotation of the rotor body (74) with respect to the needle protection member (16). A needle hub (14) has a displacement prevention portion (58a) that prevents the needle protection member (16) from being displaced from the protection position to the use position again by contacting the restriction portion (78) at the lock position.
