PROBLEM TO BE SOLVED: To provide a pretreatment instrument for transnasal endoscopes capable of reducing a burden of a patient by improving efficiency of pretreatment for transnasal endoscopes.SOLUTION: A pretreatment instrument 1 for transnasal endoscopes includes a small-diameter tube 2 having a plurality of slit holes 4, and a large-diameter tube 3 that is shorter than the small-diameter tube 2 and into which the small-diameter tube 2 can be inserted up to a prescribed position, so that the front end side thereof protrudes. The large-diameter tube 3 is provided at least at a rear end side, includes one or more side holes 8 penetrating through the side wall thereof, and has an inside diameter that can form a clearance allowing a medicinal solution to intrude therein, at the peripheral part of the side holes 8 between the inner peripheral surface thereof and the outer peripheral surface of the inserted small-diameter tube 2.
