PURPOSE: To ensure that fouled water in a sedimentation/separation chamber as a whole needs not be scooped out when scooping it out is required.

CONSTITUTION: A bag-shaped screen 7 is installed in an inflow pipe 1 in a freely detachable manner, and further, is provided in a sedimentation/separation chamber 2. This bag-shaped screen 7 is formed using a metal alone selected from among metals such as copper, copper alloy, silver or silver alloy with the properties to inhibit the growth of microbes or a compound between the metal and any other material. Therefore, a sediment can be accumulated in the bag-shaped screen 7, and the whole fouled water in the sedimentation/ separation chamber 2 needs not be scooped out simply by removing the bag- shaped screen 7 and scooping out the sediment. Besides, the bag-shaped screen 7 is made of a metal which inhibits the growth of microbes, so that a time interval when the screen is clogged becomes longer.