Stable performance over time by a screw conveyor 32 of a filtration device 1 is ensured and looseness thereof is prevented, by automatically compensating for frictional wear of an axial support section 60 of the screw conveyor 32, without repairing or replacing worn parts. The filtration device is equipped with: a filtration tank 2; a layer of particulate activated carbon 14 within the filtration tank 2; a cleansing tank 38, which is vertically placed within the filtration tank 2 and which has an opening 40 at the lower end thereof; and the screw conveyor 38 for cleansing the filtration media, which is provided within the cleansing tank 38. The screw conveyor 38 has a shaft 34, which is suspended within the filtration tank 2 from above. The upper portion of the shaft 34 is driven, and the lower portion of the shaft 34 is supported by an axial support section 60, which is fixed to the lower portion of the cleansing tank 38. The axial support section 60 is equipped with a frictional wear compensating mechanism at a portion thereof at which the shaft 34 and the axial support section 60 contact each other.