Abstract: A biological filtration apparatus comprises: a raw water introducing section for introducing raw water as water to be processed; a biological filtration section, disposed on the lower side of the raw water introducing section, for biologically purifying/refining/filtrating the raw water so as to yield processed water; a support section, disposed on the lower side of the biological filtration section, for supporting the biological filtration section, the support section having a liquid and gas permeability; and a water collecting section, disposed on the lower side of the support section, for collecting the processed water; the biological filtration section including a packed bed comprising a hollow carrier particle, made of a resin, having a true specific gravity of at least 1.01 g/ml but less than 1.2 g/ml.