A medical device that is to be inserted into a body lumen so as to break an object in the body lumen, the medical device comprising: an elongated shaft that is rotatably driven; and a deformable breaking member (60, 200, 300, 400, 500, 600, 700) that is connected to the shaft so as to be rotatable and extends along the shaft, wherein the breaking member (60, 200, 300, 400, 500, 600, 700) has a first contact portion (62, 202, 302, 402, 501A, 502A, 601A, 602A, 701A, 702A) and a second contact portion (63, 203, 303, 403, 501B, 502B, 601B, 602B, 701B), wherein the first contact portion (62, 202, 302, 402, 501A, 502A, 601A, 602A, 701A, 702A) is located more outward in a radial direction of the breaking member (60, 200, 300, 400, 500, 600, 700) than the second contact portion (63, 203, 303,403, 501B, 502B, 601B, 602B, 701B) in a state in which the breaking member (60, 200, 300, 400, 500, 600, 700) is expanded radially outward, wherein the second contact portion (63, 203, 303, 403, 501B, 502B, 601B, 602B, 701B) is located more outward in the radial direction of the breaking member (60, 200, 300, 400, 500, 600, 700) than the first contact portion (62, 202, 302, 402, 501A, 502A, 601A, 602A, 701A, 702A) in a contracted state rather than the expanded state, in the contracted state the second contact portion has a radially outward convex shape, wherein the first contact portion (62, 202, 302, 402, 501A, 502A, 601A, 602A, 701A, 702A) is located to be closer to a center portion of the breaking member (60, 200, 300, 400, 500, 600, 700) in an axial direction thereof than the second contact portion (63, 203, 303, 403, 501B, 502B, 601B, 602B, 701B) in the expanded state, wherein the breaking member has a plurality of wires and wherein positions of a connection portion on a distal side and a connection portion on a proximal side, in which a wire (61, 201, 301, 401) is connected to the shaft, are different from each other in a circumferential direction, characterized in that the second contact portion curves to have a curvature radius smaller than that of the first contact portion in the expanded state, wherein each of wires (61, 201, 301, 401) has an inflection point between the first contact portion (62, 202, 302, 402, 501A, 502A, 601A, 602A, 701A, 702A) and the second contact portion (63, 203, 303, 403, 501B, 502B, 601B, 602B, 701B) in the expanded state. an elongated shaft that is rotatably driven; and a deformable breaking member (60, 200, 300, 400, 500, 600, 700) that is connected to the shaft so as to be rotatable and extends along the shaft, wherein the breaking member (60, 200, 300, 400, 500, 600, 700) has a first contact portion (62, 202, 302, 402, 501A, 502A, 601A, 602A, 701A, 702A) and a second contact portion (63, 203, 303, 403, 501B, 502B, 601B, 602B, 701B), wherein the first contact portion (62, 202, 302, 402, 501A, 502A, 601A, 602A, 701A, 702A) is located more outward in a radial direction of the breaking member (60, 200, 300, 400, 500, 600, 700) than the second contact portion (63, 203, 303,403, 501B, 502B, 601B, 602B, 701B) in a state in which the breaking member (60, 200, 300, 400, 500, 600, 700) is expanded radially outward, wherein the second contact portion (63, 203, 303, 403, 501B, 502B, 601B, 602B, 701B) is located more outward in the radial direction of the breaking member (60, 200, 300, 400, 500, 600, 700) than the first contact portion (62, 202, 302, 402, 501A, 502A, 601A, 602A, 701A, 702A) in a contracted state rather than the expanded state, in the contracted state the second contact portion has a radially outward convex shape, wherein the first contact portion (62, 202, 302, 402, 501A, 502A, 601A, 602A, 701A, 702A) is located to be closer to a center portion of the breaking member (60, 200, 300, 400, 500, 600, 700) in an axial direction thereof than the second contact portion (63, 203, 303, 403, 501B, 502B, 601B, 602B, 701B) in the expanded state, wherein the breaking member has a plurality of wires and wherein positions of a connection portion on a distal side and a connection portion on a proximal side, in which a wire (61, 201, 301, 401) is connected to the shaft, are different from each other in a circumferential direction, characterized in that the second contact portion curves to have a curvature radius smaller than that of the first contact portion in the expanded state, wherein each of wires (61, 201, 301, 401) has an inflection point between the first contact portion (62, 202, 302, 402, 501A, 502A, 601A, 602A, 701A, 702A) and the second contact portion (63, 203, 303, 403, 501B, 502B, 601B, 602B, 701B) in the expanded state.