A medical instrument includes a rod-shaped grasp portion at a base end thereof, a functional portion used in medical practice at a front end thereof, and a shape-memory portion including a rod-shaped shape-memory alloy provided between the grasp portion and the functional portion. The grasp portion includes a holding portion having a space in which one end of the shape-memory portion is inserted from the longitudinal direction. The instrument has a gap between an outer surface of the shape-memory portion and an inner surface of the holding portion, and in bending the shape-memory portion, the shape-memory portion is capable of deforming within the range of the gap. Then, by bending, the outer surface of the shape-memory portion comes into contact with an inner edge portion of an opening of the holding portion, and thereby restricts deformation of the shape-memory portion beyond the predetermined range.