The balloon catheter is used to perform angiography, inject a liquid medicine such as a chemotherapeutic agent into a blood vessel, and vascular embolization. 
A balloon catheter was proposed as disclosed in a patent document 1 (Japanese Patent Application Laid-Open Publication No.  2005-103120) by the applicant of this application. 
The balloon catheter 1 of the patent document 1 has the double tube-structured catheter main body 3 having the inner tube 9 and the outer tube 21.  The balloon 3 is mounted on the catheter main body at its front end portion.  The injection liquid passage 23 formed between the inner tube and the outer tube communicates with the inside of the catheter main body through the opening 22 formed at the front end of the outer tube. 
A catheter provided with an expandable body is disclosed in a patent document 2 (Japanese Patent Application Laid-Open Publication No.  H09-10314).  In the catheter with the expandable body, the outer tube 1 and the inner tube 2 are coaxially disposed.  The outer tube 1 is constructed of the flexible front end part 11, the intermediate part 12 whose inner and outer diameters are larger than those of the front end part 11, and the thick proximal end part 13 whose inner and outer diameters are larger than those of the intermediate part 12.  The outer tube has the contractible and foldable expandable body 10 at the front end part 11 thereof.  The catheter is smoothly, integrally, and seamlessly formed from the front end part 11 including the expandable body 10 to the proximal end part 13.