A liquid separator is a device for separating and extracting a dispersoid and a dispersion medium from a liquid sample containing the dispersoid and the dispersion medium. The liquid separator has a liquid storage container capable of storing the liquid sample; an electrode roller including a rotary shaft, arranged to touch the liquid sample in the liquid storage container, capable of conveying the liquid sample along the outer circumferential surface thereof and rotatable about the rotary shaft; a separating member held in contact with the electrode roller for separating the dispersion medium from the liquid sample being conveyed along the outer circumferential surface of the electrode roller; and a collecting member for collecting the dispersion medium from the outer circumferential surface of the electrode roller at a position downstream of the contact position with the electrode roller and the separating member in a rotating direction of the electrode roller.