A medical device comprising: an elongated shaft portion; and an expansion body (21, 100, 110, 115, 120, 125, 130, 140) disposed in a distal portion of the shaft portion, and configured to expand and contract in a radial direction, wherein the expansion body (21, 100, 110, 115, 120, 125, 130, 140) has a hold portion (51, 102, 111, 116, 121, 127, 132) that includes a proximal side hold portion (51a, 142, 162, 171) and a distal side hold portion (51b, 144, 164, 175) and that is configured to hold a biological tissue, and a movable portion (52, 103, 112, 117) that is configured to open and close the hold portion (51, 102, 111, 116, 121, 127, 132) in a holding direction, wherein the shaft portion includes an outer shaft that holds the expansion body (21, 100, 110, 115, 120, 125, 130, 140) in the distal portion of the shaft portion, and a storage sheath that stores the outer shaft, the storage sheath movable forward to and rearward from the outer shaft in an axial direction, wherein in a central portion of the expansion body (21, 100, 110, 115, 120, 125, 130, 140) in the axial direction, a recessed portion (53, 104) is formed by the proximal side hold portion (51a, 142, 162, 171) and the distal side hold portion (51b, 144, 164, 175), and the movable portion (52, 103, 112, 117) that links both of the proximal side hold portion (51a, 142, 162, 171) and the distal side hold portion (51b, 144, 164, 175) with each other, in a state where the storage sheath is moved to a distal side of the shaft portion, the storage sheath is configured to internally store the expansion body (21, 100, 110, 115, 120, 125, 130, 140) in a contracted state, and in a state where the expansion body (21, 100, 110, 115, 120, 125, 130, 140) is stored, the storage sheath is configured to be moved to a proximal side such that the expansion body (21, 100, 110, 115, 120, 125, 130, 140) is exposed outward of the storage sheath and is brought into an expanded state in the radial direction due to a self-expanding force of the expansion body (21, 100, 110, 115, 120, 125, 130, 140), the storage sheath that stores the expansion body (21, 100, 110, 115, 120, 125, 130, 140) in a contracted state is a restriction element that maintains an open state of the hold portion (51, 102, 111, 116, 121, 127, 132), and the hold portion (51, 102, 111, 116, 121, 127, 132) is closed in the holding direction when the expansion body (21, 100, 110, 115, 120, 125, 130, 140) is exposed outward of the storage sheath, and characterised in that the proximal side expansion portion (56, 106, 141, 161, 170), the distal side expansion portion (57, 107, 143, 163), and the movable portion (52, 103, 112, 117) all expand in the radial direction when the expansion body (21, 100, 110, 115, 120, 125, 130, 140) in expanded state further expands in the radial direction. an elongated shaft portion; and an expansion body (21, 100, 110, 115, 120, 125, 130, 140) disposed in a distal portion of the shaft portion, and configured to expand and contract in a radial direction, wherein the expansion body (21, 100, 110, 115, 120, 125, 130, 140) has a hold portion (51, 102, 111, 116, 121, 127, 132) that includes a proximal side hold portion (51a, 142, 162, 171) and a distal side hold portion (51b, 144, 164, 175) and that is configured to hold a biological tissue, and a movable portion (52, 103, 112, 117) that is configured to open and close the hold portion (51, 102, 111, 116, 121, 127, 132) in a holding direction, wherein the shaft portion includes an outer shaft that holds the expansion body (21, 100, 110, 115, 120, 125, 130, 140) in the distal portion of the shaft portion, and a storage sheath that stores the outer shaft, the storage sheath movable forward to and rearward from the outer shaft in an axial direction, wherein in a central portion of the expansion body (21, 100, 110, 115, 120, 125, 130, 140) in the axial direction, a recessed portion (53, 104) is formed by the proximal side hold portion (51a, 142, 162, 171) and the distal side hold portion (51b, 144, 164, 175), and the movable portion (52, 103, 112, 117) that links both of the proximal side hold portion (51a, 142, 162, 171) and the distal side hold portion (51b, 144, 164, 175) with each other, in a state where the storage sheath is moved to a distal side of the shaft portion, the storage sheath is configured to internally store the expansion body (21, 100, 110, 115, 120, 125, 130, 140) in a contracted state, and in a state where the expansion body (21, 100, 110, 115, 120, 125, 130, 140) is stored, the storage sheath is configured to be moved to a proximal side such that the expansion body (21, 100, 110, 115, 120, 125, 130, 140) is exposed outward of the storage sheath and is brought into an expanded state in the radial direction due to a self-expanding force of the expansion body (21, 100, 110, 115, 120, 125, 130, 140), the storage sheath that stores the expansion body (21, 100, 110, 115, 120, 125, 130, 140) in a contracted state is a restriction element that maintains an open state of the hold portion (51, 102, 111, 116, 121, 127, 132), and the hold portion (51, 102, 111, 116, 121, 127, 132) is closed in the holding direction when the expansion body (21, 100, 110, 115, 120, 125, 130, 140) is exposed outward of the storage sheath, and characterised in that the proximal side expansion portion (56, 106, 141, 161, 170), the distal side expansion portion (57, 107, 143, 163), and the movable portion (52, 103, 112, 117) all expand in the radial direction when the expansion body (21, 100, 110, 115, 120, 125, 130, 140) in expanded state further expands in the radial direction.