A balloon catheter system enabling balloon stretching and deflating, and balloon stretch-releasing and inflating operations to be performed at a time with a single operation. The system includes a catheter shaft including outer and inner tubes slidable to each other and a deflatable/inflatable balloon arranged between the distal ends thereof. A solution transport path is formed between the outer and inner tubes. Anterior and posterior tanks are arranged in a handle. The tanks and the inner tube passing through the central portion thereof are slidable to each other. Stopcocks are mounted in sliding portions between the inner tube and these tanks. These tanks are connected to the inside of the balloon via the solution transport path. A piston is provided inside the posterior tank. Thus, the inner pressures of these tanks change by reciprocating the inner tube fixed to the piston, thus simplifying balloon deflating and inflating operations.
