<p>A filter device filtrating treatment liquid used for applying a specified treatment to a substrate, comprising an inlet for filling the treatment liquid, an outlet for discharging the treatment liquid filled in the filter device, and a pair of support plates for holding a flat-plate like filter element in the filter device at a position where an inlet side space and an outlet side space are partitioned from each other. Since the filter element is held by the support plates, the filter element can be prevented from being deflected in use and the treatment liquid can be stably supplied to a substrate treating device without lowering the filtration efficiency of the filter device.</p>
