A balloon catheter for medical treatments easily manufacturable at low cost by a rather simple structure by providing a smaller diameter non-profile balloon catheter by eliminating the need for adhesion and welding of a balloon and eliminating extra profile at a connection part between the balloon and a shaft, wherein PTFE may be used for the shaft, and silicone may be used for the balloon. An inside hollow shaft (3) formed of a balloon material is inserted into an outside hollow shaft (2) formed of a shaft material, and the tip part of the inside hollow shaft (3) is projected from the tip end of the outside hollow shaft (2) to manufacture a double-tube catheter shaft (2). An expandable balloon (5) is formed of the projected portion of the inside hollow shaft (3), a cap (4) is fitted to the tip of the inside hollow shaft (3), and the PTFE is used for the outside hollow shaft (2), with the silicone used for the inside hollow shaft (3).