A hyperbranch polymer is bonded to a pore surface existing on a SiO.sub.2 glass porous body, such that the hyperbranch polymer is bonded to the pore surface only at the base end moiety. The hyperbranch polymer has a first generation branched moiety branched from the base end moiety, a second generation branched moiety further branched from the first generation branched moiety, and a third generation branched moiety further branched from the second generation branched moiety. A functional group, such as sulfonic acid group, from which a proton is capable of being dissociated, is bonded by substitution to the terminal end of the third generation branched moiety.