A clamp coupling comprising: a plurality of clamp segments including respective grooves each having a U or V sectional shape, the plurality of clamp segments being connected in a ring shape with the grooves facing inward of the ring shape, the clamp segments being configured to hold a plurality of objects to be connected in the grooves and connect the objects; and a connecting section (20, 30) having a first connecting section and a second connecting section for connecting the clamp segments, wherein the first connecting section is configured to serve as a hinge that permits the clamp segments to be opened from and closed to the ring shape, wherein the second connecting section is configured to connect the plural clamp segments and to permit adjustment of a circumferential length of the plural clamp segments having the ring shape, wherein the second connecting section includes a fastening section and a contact section disposed outward of the ring shape from the fastening section, wherein the contact section connects the clamp segments at one ends thereof in direct or indirect contact with each other and includes a changing means to change a spaced distance between the one ends of the clamp segments, and wherein the fastening section includes an externally threaded body inserted through the one ends and an internally threaded body screwed with the externally threaded body for holding the one ends and fastening the clamp segments thereby to reduce the spaced distance between the one ends of the clamp segments and connect the objects held in the grooves, wherein the fastening section includes a bolt and a nut, the clamp coupling being characterized in that a seating surface of the bolt, a seating surface of the nut, and receiving surfaces of the clamp segments opposed to the respective seating surfaces are formed of a curved surface so that the seating surfaces and the corresponding receiving surfaces are in surface contact with each other if a normal direction of a plate portion of each clamp segment is inclined with respect to an axis of the bolt. a plurality of clamp segments including respective grooves each having a U or V sectional shape, the plurality of clamp segments being connected in a ring shape with the grooves facing inward of the ring shape, the clamp segments being configured to hold a plurality of objects to be connected in the grooves and connect the objects; and a connecting section (20, 30) having a first connecting section and a second connecting section for connecting the clamp segments, wherein the first connecting section is configured to serve as a hinge that permits the clamp segments to be opened from and closed to the ring shape, wherein the second connecting section is configured to connect the plural clamp segments and to permit adjustment of a circumferential length of the plural clamp segments having the ring shape, wherein the second connecting section includes a fastening section and a contact section disposed outward of the ring shape from the fastening section, wherein the contact section connects the clamp segments at one ends thereof in direct or indirect contact with each other and includes a changing means to change a spaced distance between the one ends of the clamp segments, and wherein the fastening section includes an externally threaded body inserted through the one ends and an internally threaded body screwed with the externally threaded body for holding the one ends and fastening the clamp segments thereby to reduce the spaced distance between the one ends of the clamp segments and connect the objects held in the grooves, wherein the fastening section includes a bolt and a nut, the clamp coupling being characterized in that a seating surface of the bolt, a seating surface of the nut, and receiving surfaces of the clamp segments opposed to the respective seating surfaces are formed of a curved surface so that the seating surfaces and the corresponding receiving surfaces are in surface contact with each other if a normal direction of a plate portion of each clamp segment is inclined with respect to an axis of the bolt.