A catheter including an outer conduit and an inner conduit movably disposed therein. The distal tip of the inner conduit extends beyond the distal tip of the outer conduit. An inflatable balloon has a first margin attached to the distal tip of the outer conduit, and a second margin attached to the portion of the inner conduit extending beyond the distal tip of the outer conduit. The balloon includes a middle portion, an inflatable distal side portion having at least one tapering part and an inflatable proximal side portion having at least one tapering portion. The length of proximal side portion is equal to or larger than the length of the middle portion. The distal end portion of the balloon is capable of intussuscepting upon proximal movement of the inner conduit within the outer conduit. The catheter includes an inflation/deflation port for introducing and removal of inflating fluid.