PROBLEM TO BE SOLVED: To provide a catheter capable of smoothly transmitting push-in force from the hand side to the tip side, and thereby improving operability thereof.SOLUTION: A shaft 12a of a catheter 10B includes: a small-diameter part 24a on the tip side； a large-diameter part 26 on the base end side； and a taper part 28 between the small-diameter part 24a and the large-diameter part 26. The small-diameter part 24a includes: a first region 44； a second region 46 which is adjacent to the base end side of the first region 44 and has an outer diameter smaller than that of the first region 44； and a third region 48 which is adjacent to the base end side of the second region 46 and has an outer diameter larger than that of the second region 46. The first region 44 is more flexible than the second region 46. The second region 46 is more flexible than the third region 48.
