PURPOSE: To provide an evaluation apparatus for evaluating automatically and with an on-line system agglomeration condition of a sludge in a water treating 'process.

CONSTITUTION: A means for obtaining the image information of the surface of an agglomerate by photographing the surface of a sludge under agglomerating condition by means of a television camera 19 and an image processing apparatus 20 calculating the fractal dimension by performing binary treatment to the image information obtd. by this means, are installed. It may be possible for an operator only to adjust the amt. of loading of a flocculating agent by using the calculating result of the fractal dimension as a standard and to perform an optimum control of the agglomerating condition without requiring experiences for long years for evaluation of the agglomerating condition.