<；P>；PROBLEM TO BE SOLVED: To provide a medical shaft which can well improve the operability of a medical instrument having a shaft portion, and a medical instrument equipped with the medical shaft. <；P>；SOLUTION: The outside shaft 14 of a balloon catheter includes a proximal shaft 22 and a distal shaft 21. The distal end of the proximal shaft 22 is inserted into the proximal end of the distal shaft 21. A core wire 31 is inserted into the lumen 14a of the outside shaft 14 across the boundary between the shafts 21 and 22. In this structure, the proximal shaft 22 has a reduced stiffness area 23 where a helical cut 24 is formed and a fixing wall portion 41 formed in a state projecting to the distal end from the reduced stiffness area 23. The core wire 31 is welded to the fixing wall portion 41. <；P>；COPYRIGHT: (C)2010,JPO&INPIT
