PROBLEM TO BE SOLVED: To provide a waste water treatment apparatus capable of efficiently treating nitrate nitrogen and nitrite nitrogen in waste water over a long period.SOLUTION: A waste water treatment apparatus has: a denitrification tank in which waste water is supplied from a lower part and discharged from an upper part; a plurality of network containers installed at intervals from a lower side to an upper side of the denitrification tank; and a carrier stored in the network containers, for supporting denitrifying bacteria.SELECTED DRAWING: Figure 1