Abstract: A scum sweeper for sweeping surface floating matters in a clarifying tank to a collector channel. A sweeping blade is pivotally hanged by arms to parallel endless running chains mounted onto a supporting frame installed in the tank at an above position with respect to the collector channel. A motor drives the chains that haul the blade back and forth successively over and at the surface of water in the tank. The blade always remains under the chains as a result of a free pivoting of the arms at the opposite turning end courses of the chains. Guiding arrangements are provided to lock the arms in a downward direction when the sweeping blade travels horizontally.