To improve the productivity without generating dust or damages by mounting a porous body having a flat surface portion on an upper part of a pressure vessel to which a pressurized liquid is fed so that the flat surface portion is directed upward, and allowing the pressurized liquid to be ejected through the porous body.

When a cleaning solution is fed into a pressure vessel 1 through a cleaning solution pipe 3 and filled in the pressure vessel 1, the cleaning solution is ejected from the upper surface of a porous ceramic material 2. When a glass substrate 6 is placed on the upper surface of the porous ceramic material 2, a cleaning solution layer 10 is formed therebetween and the glass substrate 6 is afloat thereon. This means that the glass substrate 6 is afloat on the porous ceramic material 2 in a non-contact condition, realizing a state of extremely small friction. Then, the cleaning solution is sprayed against the upper surface of the glass substrate 6 from a cleaning solution spray nozzle 9 to clean the glass substrate 6. In this way, both sides of the glass substrate 6 can be simultaneously cleaned.