1. An information relevance display method comprising: a search designation step which, by a search designation unit, designates element information and attribute information; a relevance information extract step which, by a relevance information extract unit, extracts attributes common to two pieces of element information as relevance information from possessed attributes of plural pieces of element information designated in the search designation step; a first network display step which, by a first network display unit, displays a first network by arranging and displaying, for the element information and the attribute information designated in the search designation step, the element information as element nodes, and by connecting with edges two element nodes possessing common attribute information by referring to the relevance information; and a second network display step which, by a second network display unit, displays a second network by converting possessed attributes of the element nodes in the first network into a display of attribute nodes for arrangement and by connecting with edges the element nodes and the attribute nodes of the possessed attributes thereof.