Abstract: A blood vessel piercing instrument includes an outer tube assembly and an inner needle assembly. The outer tube assembly has an outer tube and an outer tube hub attached to the rear end portion of said outer tube. The outer tube has a metal tubular member made of a superelastic metal and a resin tubular member which covers the outside surface of the metal tubular member and has the front end portion extending beyond the front end of the metal tubular member. The inner needle assembly includes an inner needle which is extractably inserted in said outer tube assembly and has a piercing edged surface formed at the front end protruding from said outer tube and an inner needle hub which is attached to the rear end portion of said inner needle and engages with the rear end of said outer tube hub. An inside diameter of said front end portion of said resin tubular member is smaller than the inside diameter of said metal tubular member and substantially equal to an outside diameter of said inner needle.