A surgical instrument comprising: an insert section including a distal end extension and a proximal end portion and having a first axis in a longitudinal direction; an operating section provided at the proximal end side of the insert section; and a transmitting member provided in the insert section to be capable of advancing and retracting therein; and a first grasping portion provided in the distal end extension of the insert section; and a second grasping portion biased in a direction toward the first grasping portion and being movable in a direction away from the first grasping portion, a first, conical contact surface provided at the proximal end side of the second grasping portion, and a second contact surface provided at the distal end side of the transmitting member, and movable between a first position apart from the first contact surface and a second position where, by pressing the second contact surface against the first contact surface so that the first and second contact surfaces slide over each other, a proximal end flat surface of the second grasping portion is separated from a distal end flat surface of the first grasping portion by a distance in which a suturing needle which sutures a tissue can be clamped, and wherein, when the second contact surface of the transmitting member is at the first position, the suturing needle can be held in a clamped state between the distal end flat surface of the first grasping portion and the proximal end flat surface of the second grasping portion, and wherein the first grasping portion, the second grasping portion, and the suturing needle which are integrated in the clamped state are not configured to be actively rotated through operation of the operating section but are configured to be passively rotated when an external force is applied to the suturing needle. an insert section including a distal end extension and a proximal end portion and having a first axis in a longitudinal direction; an operating section provided at the proximal end side of the insert section; and a transmitting member provided in the insert section to be capable of advancing and retracting therein; and a first grasping portion provided in the distal end extension of the insert section; and a second grasping portion biased in a direction toward the first grasping portion and being movable in a direction away from the first grasping portion, a first, conical contact surface provided at the proximal end side of the second grasping portion, and a second contact surface provided at the distal end side of the transmitting member, and movable between a first position apart from the first contact surface and a second position where, by pressing the second contact surface against the first contact surface so that the first and second contact surfaces slide over each other, a proximal end flat surface of the second grasping portion is separated from a distal end flat surface of the first grasping portion by a distance in which a suturing needle which sutures a tissue can be clamped, and wherein, when the second contact surface of the transmitting member is at the first position, the suturing needle can be held in a clamped state between the distal end flat surface of the first grasping portion and the proximal end flat surface of the second grasping portion, and wherein the first grasping portion, the second grasping portion, and the suturing needle which are integrated in the clamped state are not configured to be actively rotated through operation of the operating section but are configured to be passively rotated when an external force is applied to the suturing needle.