Continuous circulation sand filter and continuous circulation sand filtering method

Provided is a continuous circulation sand filter including a filtering barrel filled with a sand filtering layer, an inflow tube for introducing raw water into the filtering barrel, a treated water discharge part for discharging treated water purified by passing the raw water through the sand filtering layer from a lower end of the sand filtering layer to an upper end thereof, an air lift tube for transferring contaminated sand, located in the lower end of the sand filtering layer, from a lower part of the filtering barrel to an upper part thereof, a transfer water discharge filter contacting the air lift tube to discharge transfer water moved upward together with sand through the air lift tube and trap the sand and a foreign substance, a descent guide tube downwardly moving the sand and the foreign substance moved to the upper part of the filtering barrel through the air lift tube, and a foreign substance separation tube suctioning the downwardly moving foreign substance to remove the foreign substance from the downwardly moving sand, and discharging the foreign substance.