Abstract: In the catheter comprising: a balloon 11 provided with a front and a rear opening end and a thin wall made of synthetic resins; an outer tube 21; an inner tube 31 which is disposed inside the outer tube 21 and has its tip portion projected outward from the outer tube 21; and, the balloon 11 having the front and the rear opening end fixedly mounted in a water-tight manner on the inner tube 31 and the outer tube 21 to form a front fixed portion 61 and a rear fixed portion 61', respectively;a plurality of parallel-extending circumferential grooves 41 are provided to a distal area 32 of the inner tube 31, each of the circumferential grooves 41 having a predetermined length, and said distal area having a certain length which extends from said front fixed portion and over said rear fixed portion in a direction of the hub portion.