There is provided a device for attaching a one-way type pouring nozzle, which includes a simple and small-size mechanism capable of efficiently fusion-joining the one-way type pouring nozzle to a film for package bag. In this device, a nozzle template film formed with a plurality of one-way type pouring nozzles templated by tear-inducing flaws is fed to a continuously running film for package bag to fusion-join a base portion of each of the one-way type pouring nozzles through its outer sealant layer to an inner sealant layer on one-sided portion of the film for package bag, while an unwanted portion of the nozzle template film is cut out and removed. The device also includes a pair of fusion rollers pushing and fusion-joining the one-way type pouring nozzle in the nozzle template film to the running film for package bag under the running at equal speed, and the fusion roller pair is constituted with a heating roller always energizing toward the side of the running path of the film for package bag, and a heat roller for attachment provided with protrusions intermittently pushing the film for package bag to positions of one-way type pouring nozzles in the nozzle template film on the heating roller.