When a transistor including a conductive layer having a three-layer structure is manufactured, three-stage etching is performed. The file system has a plurality of items. Rotary-kiln end-wall seals according to the invention should exhibit very low wear and tear if possible and have a service life that corresponds to the maintenance intervals of the rotary kiln as much as possible. The external MOSFET turns on after a delay when power is applied during hot insertion. This provides frequency tuning in which mode hopping is suppressed.