A medical instrument has a capsule； an arm member disposed to protrude from the capsule； an operation wire connected to the arm member； a sheath configured to accommodate the operation wire； and a link configured to connect the sheath with the capsule, wherein the link has an engaging portion including a first surface intersecting with the longitudinal axis； and an engaged portion movable to an opposite position opposite to the first surface and a position spaced away from the first surface in spite of a relative position of the capsule with respect to the sheath, and configured to restrict a separation of the capsule with respect to the sheath when the engaged portion is disposed at the opposition position to contact the first surface, and wherein the capsule is rotatable in response to a rotation force from the sheath when the engaged portion is disposed at the opposition position.
