This needle assembly is provided with a needle having a needle tip, a needle hub, and a protector. The protector is displaceable between a non-protection position at which the needle is exposed and a protection position at which the needle tip is covered; has an opening formed elongated to match the needle, and includes a main body and a claw-like portion. The needle enters the main body from the opening to cover the needle tip when the protector is displaced to the protection position. The claw-like portion is bent by the needle when the protector is displaced to the protection position, allows the needle to advance into the main body, and is elastically restored to lock the needle when the needle enters the main body. The claw-like portion projects obliquely from the main body, extends across the opening in the width direction, and extends in the longitudinal direction.