To obtain an efficient culture tank damaging no bacterial cells and a culture system, in a wastewater cleaning system utilizing marine nitrifying sludge such as marine ammonia oxidizing bacteria, marine nitrous acid oxidizing bacteria or the like.

A filter device comprising hollow fiber membranes is provided in the culture tank of marine nitrifying sludge. Further, the culture system for marine nitrifying sludge is constituted of a ventilation device, a heater, a cooler, a negative ion generator, an additive supply device, the filter device comprising hollow fiber membranes and the culture tank.