To improve productivity and performance by fixing organo silicone quaternary ammonium salt to the surface of a base material formed of an organic polymer.

A base material is formed of an organic polymer such as polyethylene, polypropylene, polyurethan. Especially three-dimensional mesh-like porous body of polyurethane or the like or non-woven fabric is preferable. Organo silicone quaternary ammonium salt such as 3-(trimethoxyl) propyl dimethyl-alkyl ammonium chloride is fixed to the surface of the base material. This fixation can be favorably achieved by processing using a liquid containing organo silicone quaternary ammonium salt and a sulfate surfactant. Thus, cation is remarkably shown so that the filter can have favorable white blood cell removal and platelet removal rate at a practical bloodstream speed.