PROBLEM TO BE SOLVED: To prevent a balloon from becoming difficult to expand due to blocking. An expansion catheter 100 includes a tubular portion 111 that can be expanded and contracted in a radial direction, and a balloon 12 that is disposed outside the tubular portion and that is expanded by supplying a fluid. The balloon has an inner layer 121 that is in close contact with the outer peripheral surface of the tubular portion, and an outer layer 122 that is arranged outside the inner layer. By supplying a fluid between the inner layer and the outer layer, the outer layer is radially outward. Expand and transform. At least one of the inner layer and the outer layer is formed with a holding portion (123) that holds a space for guiding the supply of fluid between the inner layer and the outer layer. [Selection diagram] Fig. 4【課題】ブロッキングによりバルーンが拡張しにくくなることを抑制する。【解決手段】拡張用カテーテル１００は、径方向に拡縮可能な筒状部１１１と、筒状部の外側に配置され、流体の供給により拡張するバルーン１２と、を備える。バルーンは、筒状部の外周面に密着する内層１２１と、内層の外側に配置される外層１２２とを有し、内層と外層の間に流体が供給されることにより、外層が径方向外側に拡張変形する。内層および外層の少なくとも一方には、内層と外層の間に流体の供給を案内する空間を保持する保持部（１２３）が形成される。【選択図】図４
