A surgical instrument includes an insertion part； a base having a bottom part； first grasping surface； second grasping surface； a plurality of staple disposed between the base and the first grasping surface； first and second staple line consist of the plurality of staple； a groove part； a traction member； a locked part having first and second locked part； and a blade part accommodated in the groove part so as to be capable of advancing and retracting along the longitudinal axis, wherein the first and second wall surfaces are provided to be apart from each other in the cross direction such that when the blade part is positioned between the first and second locked parts in the cross direction, gaps both between the blade part and the first locked part and between the blade part and the second locked part are capable of being formed.
