A sludge trapping container has a side wall and a bottom each having a plurality of holes defined therein by electron beam machining. Each of the holes has a tapered shape such that the diameter D1 of an end thereof opening at an outer wall surface of the sludge trapping container is smaller than the diameter D2 of an end thereof opening at an inner wall surface of the sludge trapping container. The sludge trapping container is economical as it is suitable for repeated use, and can trap a sludge highly efficiently and can be cleaned highly efficiently because of the gradient of inner surfaces of the holes.