Abstract: An apparatus and method for purification and assay of neurites is useful for separation and analyses of extension organelles and/or protrusion of cells for purification, production, observation, and quantification of neurites in the neurobiology field. The present invention provides a pore-sized controlled porous filter membrane which outspace side surface is coated with a cell adhesion layer to form an adhesion surface, and combines the neuronal cells with the porous filter membrane in an aqueous environment under conditions in which outgrown neurites from cell bodies of the neuronal cells are attracted to and grow on the adhesion surface, wherein the outgrown neurites of the neuronal cells pass through pores provided in the porous filter membrane to the adhesion surface while each of the pores has a size smaller than the cell bodies of the neuronal cells so as to prevent the cell bodies of the neuronal cells passing through the pores and remaining on an opposing side surface of the porous filter membrane.