The present invention relates to a surgical instrument (10) for an endoscope. The surgical instrument of the present invention has a double tube inserted through a channel of an endoscope, wherein the double tube has an outer tube (20), and an inner tube (30, 300) inserted through the outer tube and advancing and retreating relative to the outer tube (20), and the outer tube (20) of the double tube is made from a plastic material, in which a silicone compound is added to an organic polymer, so as to reduce friction resistance between the outer peripheral surface (202, 212), which is a sliding surface, of the inner tube (30, 300) and the inner peripheral surface (204, 210), which is a sliding surface, of the outer tube to be lower than if both the outer tube and the inner tube of the double tube are made only from the organic polymer, when the inner tube advances and retreats with respect to the outer tube in a state in which the double tube is bent along a channel path.
