PROBLEM TO BE SOLVED: To provide a nitrification tank capable of effectively nitrifying ammonia and a wastewater treatment system.SOLUTION: The nitrification tank having a supply port to which water from a water tank where seafood is bred is supplied, a first perforated pipe through which the water supplied to the supply port is discharged and a plurality of cylindrical hollow filter mediums on the hollow inner surface of which nitrifying bacteria to nitrify ammonia contained in the water adhere includes: a first filter on which the respective outer surfaces of the plurality of hollow filter mediums are adjacently arranged without a gap； a second filter on which the nitrifying bacteria adhere and through which the water discharged from the first perforated pipe is roughly equally supplied from the upper side to the lower side of the respective plurality of hollow filter mediums； a second perforated pipe through which oxygen is supplied from the lower side to the upper side of the plurality of hollow filter mediums； and a discharge port from which the water obtained from the lower side of the first filter is discharged.
