FILTER DEVICE

To provide a filtration device capable of stably filtrating a liquid to be treated at a constant flow rate, the filtration device including a single or a plurality of continuous first units including a first separation membrane part that separates a liquid to be treated in a first storage tank into a first permeated liquid and a first non-permeated liquid, a first extraction pipe through which the first non-permeated liquid is extracted, a first adjustment unit that adjusts a flow rate of the first permeated liquid to be substantially constant, and a first liquid scale that detects a liquid amount in the first storage tank, a second unit including a second separation membrane part that separates a stored liquid in a second storage tank storing therein the first permeated liquid into a second permeated liquid and a second non-permeated liquid, a second extraction pipe through which the second non-permeated liquid is extracted, a second adjustment unit that adjusts a flow rate of the second permeated liquid to be substantially constant, and a second liquid scale that detects a liquid amount in the second storage tank, a first controller unit that controls the liquid amount in the first storage tank based on measurement values from continuous two first units or from the continuous first and second units, and a second controller unit that controls the liquid amount in the second storage tank based on a measurement value from the second unit.