PROBLEM TO BE SOLVED: To provide a catheter which has two lumens, is reduced in diameter at the distal end thereof, and keeps rigidity enough to insert the lumens even into the narrow spots of tubular organs.SOLUTION: The catheter 10 includes a first lumen 11 and a second lumen 12. The first lumen 11 forms a pathway from the proximal end to the distal end of the catheter and has one aperture at the distal end of the catheter. The part having a determined length from the distal end of the catheter is a diameter-reduced part 17 which is reduced in diameter via a tapered step part 15 to keep a tube containing the first lumen 11. The second lumen 12 forms a pathway from the proximal end to the step part 15 of the catheter and has another aperture at the step part 15. On the outer circumference of the diameter-reduced part 17, there is formed a groove part 20 which is so shaped that a part of the internal circumference of the aperture 15a extends from the aperture 15a of the step part 15 along the direction of the axial center F of the second lumen 12.
