A needle assembly is disclosed, which includes a needle protection member and a rotor. The rotor has a rotor body and a restriction portion. When the needle protection member in the initial state is displaced from the protection position to a use position and returns to a protection position, the restriction portion is displaced from the initial position to the lock position by the rotation of the rotor body with respect to the needle protection member. A needle hub has a displacement prevention portion that prevents the needle protection member from being displaced from the protection position to the use position again by contacting the restriction portion at the lock position.
