It is intended to build a mechanism similar to that of the efficient purification system of rivers. By a pump unit, water circulation corresponding to the natural water circulation generated by water evaporation and rainfall is produced to generate a water flow in a biological filtration layer including a useful purification bacterial group. Thus, an extremely-high-efficient purification device as compared to a typical system and an aquarium integrally incorporating the device are provided. A purification device of the present invention includes a low-water-permeable biological filtration layer configured to purify water, and a pump unit configured to generate a water flow in the biological filtration layer. The biological filtration layer includes a useful purification bacterial group having grown bacteria for performing purification. The useful purification bacterial group is fixed in a bulk state.
