A needle assembly for introducing an indwelling catheter into a blood vessel of a patient is disclosed. The needle assembly is provided with a handle having an outer sleeve (3), an inner sleeve (13) coaxially fixed to the outer sleeve, and a gap between the outer sleeve and the inner sleeve； a hollow needle (9) configured to pierce the patient to guide the catheter into the blood vessel； a needle hub fixed to the needle and movably fit in the handle, which is temporarily retained at a first position where the needle is exposed out of the handle and biased to move toward a second position where the needle retracts in the handle； a release (19) configured to releasably retain the needle hub at the first position； and a passageway composed of a first through hole (23) penetrating the inner sleeve and a second through hole (21) penetrating the needle hub. These first through hole and the second through hole are so formed as to align with each other to allow flashback of blood from the needle to the gap of the handle without a mediating member between the first through hole and the second through hole only if the needle hub is at the first position.
