A surgical instrument used in a cutting operation of a trabecular meshwork, the surgical instrument comprising a probe, wherein the probe comprises: an outflow port which flows out a cleaning liquid toward the trabecular meshwork corresponding to a cut position; a suction port which is formed in a side surface of said probe, collects the cleaning liquid flowed out of said outflow port as a waste liquid, and sucks the trabecular meshwork into an inner portion of the probe; a cutting portion which cuts the trabecular meshwork sucked into the suction port; and the probe having a high rigidity, and the probe further comprising: an attaching portion (310, 320) for attaching said surgical instrument; a protection portion which is arranged closer to a leading end side of said probe than said suction port and the cutting portion, has such a shape as to be extended to a side surface forming said suction port in the leading end of said probe, and protects an outer wall of the canal of Schlemm corresponding to a non-cut position from the cutting and the suction by being positioned between said cutting portion and the outer wall of the canal of Schlemm during the cutting of the trabecular meshwork by said cutting portion; and characterized in that the probe comprises: an adjusting portion which adjusts a distance between said protection portion and said suction port in a state of being attached to said probe by said attaching portion. an outflow port which flows out a cleaning liquid toward the trabecular meshwork corresponding to a cut position; a suction port which is formed in a side surface of said probe, collects the cleaning liquid flowed out of said outflow port as a waste liquid, and sucks the trabecular meshwork into an inner portion of the probe; a cutting portion which cuts the trabecular meshwork sucked into the suction port; and the probe having a high rigidity, and the probe further comprising: an attaching portion (310, 320) for attaching said surgical instrument; a protection portion which is arranged closer to a leading end side of said probe than said suction port and the cutting portion, has such a shape as to be extended to a side surface forming said suction port in the leading end of said probe, and protects an outer wall of the canal of Schlemm corresponding to a non-cut position from the cutting and the suction by being positioned between said cutting portion and the outer wall of the canal of Schlemm during the cutting of the trabecular meshwork by said cutting portion; and characterized in that the probe comprises: an adjusting portion which adjusts a distance between said protection portion and said suction port in a state of being attached to said probe by said attaching portion. an attaching portion (310, 320) for attaching said surgical instrument; a protection portion which is arranged closer to a leading end side of said probe than said suction port and the cutting portion, has such a shape as to be extended to a side surface forming said suction port in the leading end of said probe, and protects an outer wall of the canal of Schlemm corresponding to a non-cut position from the cutting and the suction by being positioned between said cutting portion and the outer wall of the canal of Schlemm during the cutting of the trabecular meshwork by said cutting portion; and characterized in that the probe comprises: an adjusting portion which adjusts a distance between said protection portion and said suction port in a state of being attached to said probe by said attaching portion.