1. An information filtering apparatus, comprising: information indicating means for indicating pieces of learning information; learning information control means for receiving a plurality of teaching signals respectively indicating whether one piece of learning information indicated by the information indicating means is necessary or unnecessary and generating pieces of teaching data respectively composed of one piece of learning information and one teaching signal corresponding to the piece of learning information; learning means for performing a learning operation for each of the pieces of teaching data generated by the learning information control means to produce records indicating whether each piece of learning information indicated by the information indicating means is judged to be necessary or unnecessary; and information filtering means for filtering pieces of information data according to the records produced by the learning means to arrange the pieces of information data in order of necessity.