PURPOSE: To obtain a cleaning filter with a longer life by providing a spool filter to trap suspended substances in a solution and a metal screen filter on the entry side of the solution to ensure cleaning after use.

CONSTITUTION: Metal screen filters 35a, 35b and 35c are arranged on the entry side of a solution of a spool filter 34 to trap suspended substances in the solution. The mesh size of the metal screen filters 35a, 35b and 35c is the same as or larger than that of the spool filter 34. The mesh size of the metal screen filters 35a, 35b and 35c laminated is made smaller gradually as it approaches the spool filter 34. One example is the metal screen filters 35a, 35b and 35c made of stainless steel.