[PROBLEMS] To provide a high-performance filter which can realize a high collection efficiency without increasing the weight per unit area which leads to an increase in pressure loss of the filter by using a nonwoven fabric having a nano-order fiber diameter and subjected to charging treatment. [MEANS FOR SOLVING PROBLEMS] A filter comprising a nonwoven fabric comprising fibers having a diameter of 0.001 to 1 µm subjected to charging treatment is produced by preparing a solution composed mainly of a polymer and an organic solvent, spinning the solution by a charge spinning method, and then collecting the resultant polymer fibers on a collecting substrate, and stacking another layer onto the assembly.
