A balloon-equipped catheter having a variable stiffness insertion section comprises: an insertion section provided with a coil-shaped member which can be stretched, has a predetermined elastic force, and has a predetermined compressed length, and also with a sheath which is a tube body having a fluid pipe path and having predetermined flexibility, the sheath being provided with a sheath body surrounded by the coil-shaped member, and also with a sheath end section which is provided to one end side of the sheath body, has a greater diameter than the sheath body, and has a contact surface with which one end surface of the coil-shaped member is in contact, one opening of the fluid pipe path being provided in the sheath end section, the other opening of the fluid pipe path being provided on the other end side of the sheath body an inflatable balloon provided to the sheath end section of the sheath and configured in such a manner that, when fluid is supplied to the balloon through the one opening of the fluid pipe path, the balloon is inflated so that the balloon has an outer diameter greater than the outer diameter of the sheath end section, and also in such a manner that, when the fluid is discharged through the one opening, the balloon contracts and comes into close contact with the outer peripheral surface of the sheath end section and an operation section installed and affixed to the other end side of the sheath and provided with an operation section body and a slide member, the operation section body being provided with a fluid supply/discharge device connection section which is directly or indirectly connected to a fluid supply/discharge device for supplying the fluid into the balloon through the fluid pipe path or discharging the fluid within the balloon through the fluid pipe path, the slide member being slidably disposed on the inner peripheral surface side of the operation section body and disposed on the other end side of the operation section body by the elas
