A filtration device includes a continuous first unit including a first membrane that separates a liquid into first permeated and non-permeated liquids, a first adjuster that adjusts a flow rate of the first permeated liquid to be substantially constant, and a first liquid scale that detects a liquid amount, a second unit including a second membrane that separates another liquid into second permeated and non-permeated liquids, a second adjuster that adjusts a flow rate of the second permeated liquid to be substantially constant, and a second liquid scale that detects another liquid amount, a first controller 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 that controls the another liquid amount based on a measurement value from the second unit.