To clean a printing block thoroughly by solidifying polyimide resin as a film and oscillating an orientation film printing block substantially in parallel with the oscillatory plane of ultrasonic wave thereby peeling OFF the polyimide solidification film ultrasonically from the orientation film printing block. SOLUTION: An ultrasonic oscillator 11 having a substantially rectangular laterally elongated oscillatory plane is disposed closely to the water surface in a solidifying/peeling tank 1 and fixed to the wall of the tank 1 such that the longitudinal direction of the oscillatory plane will be substantially in parallel with the water surface. A circulation pump 14 is coupled through circulation piping 15 in order to circulate cleaning water 16 overflowing 12 into the cleaning tank back to the solidifying/peeling tank 1 after removing foreign matters therefrom through a filter section 13. Polyimide resin of the orientation film printing block 5 is solidified by immersing the printing block 5 into the cleaning liquid 16 in the cleaning tank and then the printing block 5 is oscillated substantially in parallel with the oscillatory plane of ultrasonic wave thus peeling OFF the polyimide solidification film from the printing block 5.
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