A balloon catheter system includes: a light irradiation probe including, at a distal end portion of a fiber probe, a light irradiation portion for irradiating light； a balloon catheter including a shaft having a through hole through which the light irradiation probe is insertable, the through hole allowing liquid feeding, with the light irradiation probe being arranged, and a balloon provided to the shaft and configured to be expandable and contractable by a liquid injected into the balloon； and an injection apparatus including a measuring portion capable of measuring a quantity of the liquid, and an injection portion for injecting the liquid measured by the measuring portion into the balloon, and the balloon expands by the injected liquid, to thereby extend a wall of a region to be treated and retain the wall of the region to be treated in an extended state.
