1. A clustering apparatus comprising: a similarity degree calculating section configured to calculate a similarity degree of a combination of optional two of objects to store the calculated similarity degree in a similarity degree table, excluding a combination of one of the optional two and itself; a merging object selecting section configured to select as merging objects, two objects related to the similarity degree which satisfies a predetermined reference; a new object generating section configured to generate a new object from said merging objects; a merging object removing section configured to remove from said similarity degree table, a similarity degree between each of said two objects selected as the merging objects and each of the objects; and a new object adding section configured to calculate a similarity degree between said new object and each of said objects other than said new object.