To provide a method of mounting the nozzle of an endoscope that can reduce time required for mounting an air and water supply nozzle, and simplify the air and water supply nozzle mounting work.

When an air and water supply nozzle 7 has been inserted detachably into the mounting hole 8 of a front end component portion 2, a thermoplastic filling member 10 is disposed in the part exposed at least to the front end side of the spaced between the mounting hole 8 of the front end component portion 2 and the air and water supply nozzle 7. In addition, the filling member 10 is heated and melted by heat conduction from the air and water supply nozzle 7 heated with a heating tool and the filling member 10 and is filled into the space between the air and water supply nozzle 7 and the mounting hole 8.