PURPOSE: To easily separate and remove a liquid crystal mixed in a washing liquid by passing the washing liquid mixed with the liquid crystal through a filtering medium.

CONSTITUTION: A material to be cleaned, for example, a glass substrate 5 with deposition of a liquid crystal is dipped in a washing tank 4 containing a washing liquid 3 comprising 7-8% detergent soln. The washing tank 4 is equipped with a vibrator 2 at the bottom driven by an oscillator 1. Then the vibrator 2 is vibrated so that the liquid crystal depositing on the surface of the glass substrate 5 is washed out by ultrasonic from the vibrator and by the washing power of the detergent in the detergent liquid. The washing liquid mixed with the liquid crystal overflows into an annular receiving part 6 attached to the upper side wall of the washing tank 4 and is sent to a concentrating tank 7 of liquid crystal through a pipe. By driving a pump 8, the soln. in the concentrating tank 7 is sent to a ultrafiltering membrane 9 under pressure, where the soln. is divided into a liquid crystal component emulsified in the soln. and an almost pure washing liquid.