A medical guide wire having a core wire formed of a flexible elongate member, a helical spring body inserted to a distal end portion of said core wire to be placed around said core wire, and a head plug provided at distal end tips of both said core wire and said helical spring body by means of a welding member, and a synthetic layer coated at least on an outer surface of a proximal portion of said core wire, characterised by said core wire made of austenitic stainless steel wire treated with a solid solution procedure, and drawn at a wire-drawing procedure and then heat treated at low temperature of 400°C - 495°C, said solid solution procedure meaning to put a crystalloid element into a solid solution wire; a final wire-drawing procedure defined after repeating at least more than a single set of procedures, wherein each single set comprises a combination of said wire-drawing procedure and said heat-treating procedure; said core wire being rendered with a whole cross sectional reduction ratio as 90%-97.6% until said core wire is subjected to said final wire-drawing procedure; said core wire having 8% or more as a total increase rate of a tensile rupture strength attained due to said heat treatment procedure until said core wire is subjected to said final wire-drawing procedure; said core wire being subjected to turns of twist at low temperature of 380°C - 495°C due to an electrical resistance caused by energizing said core wire after finishing said final wire-drawing procedure; said core wire being heat treated at low temperature of 340°C - 420°C with the use of a heat generated when said synthetic layer is coated on said outer surface of said core wire after treating said distal end portion of said core wire with a mechanical procedure including grinding or pressing procedure; said core wire having 8% or more as a total increase rate of a tensile rupture strength attained each time when said core wire is subjected to said heat treatment procedure after said core wire is subjected to said final wire-drawing procedure; said core wire having 10% or more as a total increase rate of a tensile rupture strength attained each time when said core wire is subjected to said heat treatment procedure, so as to obtain said tensile rupture strength as 260kgf/mm2 - 350kgf/mm2; said core wire and said helical spring body being bonded by a welding member, said welding member being formed by a eutectic alloy having a melting temperature of 180°C - 495°C; said core wire being drawn by said final wire-drawing procedure, said turns of twist, and being heat treated at low temperature in which said tensile rupture strength reaches a maximum to provide said core wire with a high tensile rupture strength and high straightness; and said tensile rupture strength being represented by P1/Sp, in which P1 is a magnitude of a tensile force applied when the core wire surrenders to disconnection, and Sp is a cross sectional area of said core wire when said core wire surrenders to disconnection; wherein said whole cross sectional reduction ratio means a reduction rate R expressed by R=(S1-S2)/S1, in which S1 is a cross sectional area regarding an original diameter of said core wire treated with said solid solution procedure before said core wire is drawn, and S2 is a resultant cross sectional area regarding a finished diameter of said core wire after said core wire is finally drawn during said drawing process; wherein said austenitic stainless steel wire has chemical composition as follows: C: less than 0.15% by weight, Si: less than 1.0% by weight, Mn: less than 2.0% by weight, Ni: 6%-16% by weight, Cr: 16%-20% by weight, P: less than 0.045%, S: less than 0.030%, Mo: less than 3.0%, balance: iron and impure substances unavoidably contained.