To provide a full automatic filtering device which has an agitating aeration cleaning function due to a sterilizer and a sterilizing and back washing function due to fine air for effectively removing slime, such as biofilms, and SS in a filter tank in various types of water treatment of a warm bath facility, an aquarium, etc.

A chemical cleaning mode is installed at a rotation stop position (a limit position) of an automatic five-way valve to facilitate the auto-injection of the sterilizer. Pressure air of a compressor and a two liquids-mixing nozzle are used to enable aeration cleaning where air containing the sterilizer is fed from the tank bottom. An air injection nozzle for back washing is used to enable sterilizing back washing where sterilization and back washing using high concentration chlorine, povidone iodine etc. are carried out at the same time.

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