A medical hollow needle assembly includes an outer cylindrical body including a through-hole; a hollow needle having an outer peripheral surface, wherein a proximal portion of the hollow needle is disposed in the through-hole of the outer cylindrical body, and wherein the outer peripheral surface of the hollow needle has an outer reduced-diameter surface that has a smaller outer diameter than that of a more proximal portion of the outer peripheral surface of the hollow needle; and an inner cylindrical body including an insertion hole in which the hollow needle is disposed, wherein the inner cylindrical body is disposed between the hollow needle and an inner peripheral surface of the through-hole of the outer cylindrical body, and wherein the inner cylindrical body joins the outer cylindrical body and the hollow needle.