Abstract: A porous cross-linked copolymer of chloromethylstyrene and divinylbenzene having a divinylbenzene unit represented by Xm of from about 9.0 percent by mole to about 17.0 percent by mole based on the total moles of monomer units; a content of active chlorine atom of from about 5.25-0.08 Xm mmole/g-dry resin to about 6.43-0.10 Xm mmole/g-dry resin; a water regain of from about 0.10 ml/g-dry resin to about 1.20 ml/g-dry resin; and a total volume of micro pores having a diameter of from about 500 angstroms to about 3000 angstroms of from 0.10 ml/g-dry resin to about 1.20 ml/g-dry resin; and a porous iminodiacetic acid type chelating resin having a Xm of from about 9.0 percent by mole to about 17.0 percent by mole based on the total moles of all monomer units; an ion exchange capacity of from about 5.35-12.0 Xm/(205.6-1.30 Xm) meq/g-dry resin to about 7.93-18.1 Xm/(247.1-2.0 Xm) meq/g-dry resin; a water regain of from about 0.60 ml/g-dry resin to about 2.