To reduce a space for processing muddy water and make transport of mud easy.

A reaction tank 10 in which a flocculant cagulating mud is mixed with muddy water and the water and mud are let flow while separatively reacting them, is inclinedly arranged, and a water discharge port 13 and a mud discharge port 14 respectively discharging water and mud are provided on the lower end of the inclination. Meanwhile, a carrying conveyor unit 20 circulatingly moving a mesh-like carrying belt 21 of which both sides are made coarse and the center part is made fine for carrying muddy water from the mud discharge port 14 while separating it into water and mud, is arranged on the lower part of the reaction tank 10. Hereby a large storage reservoir is unnecessary to be formed, and a wide installation space is unnecessary. Even in a densely built-up district and the like, muddy water separation process is efficiently performed only by carrying in and providing this device, without possibility causing an environmental problem and much cost and time become unnecessary. Further, separated water is surely not accumulated on the conveyor, and hence the muddy water processing efficiency is improved.