In a vessel (2) to which waste liquid (11) which contains ink pigment, water and cleaning liquid used in a printer is supplied, a metal electrode plate (30a, 30b) which allows the waste liquid (11) to flow therethrough is disposed to partition the inside of the vessel (2) into a first region (a) and a second region (b). A high voltage from a high-voltage power supply (7) is applied to the metal electrode plate (30a, 30b) while a grounding electrode (20) is connected to the first chamber (a) to generate an electrostatic field between the metal electrode plate (30a, 30b) and the grounding electrode (20) so that the water and the ink pigment are electrostatically agglomerated from the waste liquid (11) making use of electrophoresis of the ink pigment by the electrostatic field thereby to separate the waste liquid in the first region (a) into the cleaning liquid, water and ink pigment.