To provide a filtration apparatus which can provide high-quality treated water and, at the same time, can realize continuous filtration operation for a long period of time.

In this filtration apparatus 10, raw water is supplied from the top of a filtration tank 12, and the treated water is discharged from the bottom of the filtration tank 12. A filter medium packing part 15 packed with a filter medium 14 and a washing device 16 for allowing the filter medium 14 in the upper layer part of the filter medium packing part 15 to be floated for washing are provided within the filtration tank 12. Therefore, the filter medium 14 in the upper layer part of the filter medium packing part 15 is washed during filtration operation as in a travelling grate type, while the remaining part of the filter medium 14 conducts filtration in a fixed state as in a fixed bed type.