It is an object of the present invention to provide a basic crosslinked polymer having excellent ion exchange and catalyst properties with high resistance to thermal degradation which is, therefore, useful for a broad range of application, a method for producing said crosslinked polymer with great ease and high efficiency, and methods of using said crosslinked polymer.A crosslinked polymer having a tertiary amine and/or a quaternary ammonium salt structure, said crosslinked polymer has a tertiary amine structure at either end of at least one crosslink structure.