To provide a base filtration device to be installed in the bottom face of an aquarium, having a conducting tube stood by a filtration unit and returning the water after filtration to the aquarium, and installed in the filtration unit so as to be slidable and turnable to enable the position regulation of the conducting tube based on the filtration unit to be carried out easily.

The base filtration device is constituted as follows. A water-sucking part communicating a water-sucking chamber present in the inside thereof with an air pump P is installed in the filtration unit UB installed in the base of the aquarium V. The water-sucking part 3 is rotatable based on the filtration unit UB, and has a slidable water-sucking joint J. The conducting tube 30 communicating with the air pump P is connected to the water-sucking joint J so that the conducting tube 30 may be turned and regulated by sliding based on the filtration unit UB.