PURPOSE: Complete regeneration by providing freely fixable and detachable sand filter pipe for surface layer.

CONSTITUTION: A filtering layer 1 for finer sands among sands which are irregular fine porous aggregate, is placed in a sand filter pipe 3 which is freely fixable and detachable. Feed water containing suspended matter is supplied to a filtering appratus. The feed water is passed through the filtering layer 1 for fine sands and filtering layers (21 to 23) for sands having larger particle size to uptake the suspended matter and to flow out as the purified water. The filtering layer 1 which is blockaged heaviest, is removed from the sand filter pipe 3 and can freely be washed to completely remove the uptaken solids and suspended matter. Thus, the apparatus can completely be regenerated, and it is not necessary to provided a purifying means for the surface layer within the filtering apparatus. The whole apparatus can be simplified.