A thin film transistor has a semiconducting layer comprising a semiconductor and a mixture enriched in metallic carbon nanotubes. Fluid to be filtered is exposed to a filter media included in the filter module and mounted in a filter chamber provided in the filter receiver. In the laminated structure, an adhesive layer made of ITO, a reflective layer made of silver or an alloy containing silver, and a barrier layer made of ITO are layered in this order from the substrate side. A reverse bias is applied between the gate and source of the transistor in such timing that the operation is not disturbed so that the variations in the threshold voltage are suppressed. At least one LDD region of the first conductivity type is disposed in the semiconductor region between every two adjacent well regions such that the at least one LDD region is in contact with the two adjacent well regions between which it is disposed.