PURPOSE:To visually perceive quickly the back flow of blood for further facilitating treatment by providing a blood back flow inlet in an inner needle and further another one in a position closer to the tip of an outer needle other than the bore of the inner needle. CONSTITUTION:An inner needle 3 made of a metal is provided with a tubular base 41 made of a synthetic resin. An outer needle 2 made of a transparent synthetic resin slidably sticks to and covers the outer peripheral surface of the inner needle 3, exposing the proximity of the edge root of the inner needle 3 and has the base 42 attached to the tip of the base 41. A groove 7 of arbitrary length is formed in the longitudinal direction on the outer peripheral surface of the inner needle 3 up to the proximity connected to the base 41 of the inner needle from the edge root 6 of the inner needle 3 to be opened upward. The back flow of blood in the groove 7 on the surface of the inner needle 3 can be seen visually through the outer needle 2 made of the transparent synthetic resin since the early period so that, at that time, the tip of the outer needle 2 reaching at least the interior of the vein wall can be confirmed. When the inner needle 3 is drawn out after the whole needle retained in the vein is advanced only slightly in the vein, the outer needle 2 can surely be retained in the vein.
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