PROBLEM TO BE SOLVED: To provide a catheter capable of easily guiding a catheter introduced into a blood vessel of an arm to a blood vessel of a lower limb. SOLUTION: A total length L1 of a distal shaft portion 18 of a catheter 10 is longer than a total length L2 of a proximal shaft portion 20, and at least a part of the proximal shaft portion 20 with respect to an axial direction of the proximal shaft portion 20. A plurality of slits 26 extending in the intersecting direction and penetrating from the outer peripheral surface to the inner peripheral surface of the proximal shaft portion 20 are formed. In the treatment method using the catheter 10, the proximal shaft portion 20 is positioned at least at a part of the curved portion of the blood vessel that connects the blood vessel of the arm and the aorta. [Selection diagram] Figure 1【課題】腕の血管に導入したカテーテルを下肢血管まで容易に導くことができるカテーテルを提供する。【解決手段】カテーテル１０の先端シャフト部１８の全長Ｌ１は、基端シャフト部２０の全長Ｌ２よりも長く、基端シャフト部２０の少なくとも一部には、基端シャフト部２０の軸線方向に対して交差する方向に延在するとともに基端シャフト部２０の外周面から内周面まで貫通した複数のスリット２６が形成されている。カテーテル１０を用いた治療方法では、基端シャフト部２０を腕の血管と大動脈とを繋ぐ血管の湾曲した部位の少なくとも一部に位置させる。【選択図】図１
