A multi-cage type ballast water filtering apparatus having a function of automatically controlling simultaneous backwashing, the apparatus comprising: a body into or from which ballast water is drawn or discharged; and a plurality of filtering units connected to each other to form a packaged structure in the body, wherein each of the filtering units comprises a filter filtering ballast water that flows through the body, and an automatic washing unit backwashing the inner circumferential surface of the filter to remove foreign substances adhering to the filter, the apparatus further comprising: a first pressure sensor measuring a pressure in space between the body and the filters; a second pressure sensor installed on each of some of the filtering units, the second pressure sensor measuring a pressure in the filter of the corresponding filtering unit; and a control unit operating the automatic washing units of all of the filtering units when a difference between a pressure value measured by the first pressure sensor and a pressure value measured by the second pressure sensor exceeds a predetermined range, characterized in that a predetermined number of filtering units are selected in a sequence starting from highest in pressure in the filter of each of the filtering units when the filtering apparatus is operated, and the second pressure sensor is installed on each of only the selected filtering units, and that the number of second pressure sensors is less than that of the filter units. a body into or from which ballast water is drawn or discharged; and a plurality of filtering units connected to each other to form a packaged structure in the body, wherein each of the filtering units comprises a filter filtering ballast water that flows through the body, and an automatic washing unit backwashing the inner circumferential surface of the filter to remove foreign substances adhering to the filter, the apparatus further comprising: a first pressure sensor measuring a pressure in space between the body and the filters; a second pressure sensor installed on each of some of the filtering units, the second pressure sensor measuring a pressure in the filter of the corresponding filtering unit; and a control unit operating the automatic washing units of all of the filtering units when a difference between a pressure value measured by the first pressure sensor and a pressure value measured by the second pressure sensor exceeds a predetermined range, characterized in that a predetermined number of filtering units are selected in a sequence starting from highest in pressure in the filter of each of the filtering units when the filtering apparatus is operated, and the second pressure sensor is installed on each of only the selected filtering units, and that the number of second pressure sensors is less than that of the filter units. a first pressure sensor measuring a pressure in space between the body and the filters; a second pressure sensor installed on each of some of the filtering units, the second pressure sensor measuring a pressure in the filter of the corresponding filtering unit; and a control unit operating the automatic washing units of all of the filtering units when a difference between a pressure value measured by the first pressure sensor and a pressure value measured by the second pressure sensor exceeds a predetermined range, characterized in that a predetermined number of filtering units are selected in a sequence starting from highest in pressure in the filter of each of the filtering units when the filtering apparatus is operated, and the second pressure sensor is installed on each of only the selected filtering units, and that the number of second pressure sensors is less than that of the filter units.