An electrophotographic image forming apparatus includes a process cartridge which is mounted on a pull-out type cartridge tray to enable front access. The method includes a process for printing, in a prescribed pattern, a mixed solution containing a good solvent having solubility to a binder good solvent, a thermosetting binder resin, and a conductive filler. There can be provided a small-size piezoelectric oscillator which has an excellent jitter characteristic of an oscillation waveform and can stably and satisfactorily perform high-frequency oscillation utilizing overtone oscillation, and whose characteristic is easily changeable to provide excellent versatility and noise resistance.