The instrument comprises a supporting part and a staple-receiving part connected pivotally to each other, their working ends carrying opposing longitudinal jaws. The longitudinal jaw of said staple-receiving part accommodates staple magazines. Made in said staple magazines in opposition to the staple-clinching indentations of the longitudinal jaw of the supporting part are transverse slots adapted to accommodate the members for driving said staples and said staples, and longitudinal slots adapted to accommodate bars with wedge-shaped ends facing said staple-driving members, adapted for cooperation with said staple-driving members, to drive out and insert said staples. The longitudinal slot of said staple-receiving part movably accommodates a knife blade movable jointly with said bars. The instrument includes a latch-type lock for retaining the two parts in a position where they are brought together to define a suturing gap therebetween, and means for preventing substantial traumatism of the layer-by-layer sutured organs and for ensuring the rigidity of the suturing unit of the instrument in the course of a suturing operation.