Abstract: The invention relates to an instrument (10) intended to be used to modify the volume of the stomach of a patient. The invention is characterized in that the instrument comprises: a body (12) having a distal end (12a); a clamping device (16) comprising first (18) and second (20) arms pivotably mounted at the distal end (12a) of the body (12) while pivoting relative to each other, each of the first and second arms (18, 20) comprising a plurality of guides for passage of a suture needle; an opening device (30) for moving the first and second arms (18, 20) apart from each other by having them pivot relative to each other, said opening device comprising a spring member (32) connecting the first and second arms (18, 20) and tending to keep them apart from each other; and a closing device (40) for bringing the first and second arms (18, 20) together by having them pivot relative to each other.