PURPOSE: A liquid separating apparatus which can rapidly be operated by carrying out the supply of liquid to be separated and the discharge of concentrated liquid through a change-over valve having two-route passage and providing the change- over valve equipped with a strainer.

CONSTITUTION: When a change-over valve is usually in operation, a first port 14 is connected to a second port 19 through a passage 18 which is not equipped with a strainer 23, and a third port 20 is connected to a fourth port 21 through a passage 17 equipped with the strainer 23. Under such condition soft ball is not fed to a tubular membrane separator 25, but confined within the strainer 23. In order to clean the inside of the tubular membrane separator 25, the first port 14 is connected to the second port 19 through the passage 17 equipped with strainer 23 by revolving the axis 22 of the change-over valve 13. By this means, the soft ball within the strainer 23 is introduced into the tubular membrane separator 25 by means of liquid to be separated from a pressure pump 11, and the cleaning is carried out.