A candle-type ballast-water filtering device, comprising: a housing having an inlet portion and an outlet portion that allows ballast water to flow into and out of a vessel; a filter portion located in the housing to filter original ballast water introduced through the inlet portion; and an automatic washing portion washing foreign substances off of the filter portion, wherein the automatic washing portion is located in a lower portion of the filtering device, and comprises a suction portion that sucks backwash water containing foreign substances attached to the filter portion, a driving portion that is connected to the suction portion to rotate the suction portion, and a discharging portion that accommodates a side of the suction portion and discharges backwash water sucked by the suction portion, the filter portion comprises one or more filter elements for filtering and backwashing, the filter elements being arranged along concentric paths (237', 237", 237"') around a driving shaft of the driving portion, the suction portion comprises one or more flushing arms that rotate around the driving shaft by the driving portion to communicate with the respective filter elements on the concentric paths (237', 237", 237"') of the filter portion and thereby receive backwash water, the driving portion is located in a lower portion of the housing to be connected to the suction portion via the driving shaft, and the discharging portion comprises a discharge line passing through a side surface of the lower portion of the housing and a back-pressure prevention tank on the discharge line that is provided under the suction portion to communicate therewith, so that backwash water and foreign substances of the discharge line are primarily stored in the back-pressure prevention tank. a housing having an inlet portion and an outlet portion that allows ballast water to flow into and out of a vessel; a filter portion located in the housing to filter original ballast water introduced through the inlet portion; and an automatic washing portion washing foreign substances off of the filter portion, wherein the automatic washing portion is located in a lower portion of the filtering device, and comprises a suction portion that sucks backwash water containing foreign substances attached to the filter portion, a driving portion that is connected to the suction portion to rotate the suction portion, and a discharging portion that accommodates a side of the suction portion and discharges backwash water sucked by the suction portion, the filter portion comprises one or more filter elements for filtering and backwashing, the filter elements being arranged along concentric paths (237', 237", 237"') around a driving shaft of the driving portion, the suction portion comprises one or more flushing arms that rotate around the driving shaft by the driving portion to communicate with the respective filter elements on the concentric paths (237', 237", 237"') of the filter portion and thereby receive backwash water, the driving portion is located in a lower portion of the housing to be connected to the suction portion via the driving shaft, and the discharging portion comprises a discharge line passing through a side surface of the lower portion of the housing and a back-pressure prevention tank on the discharge line that is provided under the suction portion to communicate therewith, so that backwash water and foreign substances of the discharge line are primarily stored in the back-pressure prevention tank.