PROBLEM TO BE SOLVED: To provide a filter body that can prevent clogging, a filter device having the same, and a ballast water treatment apparatus that treats water by this filter device.SOLUTION: The filter body, which captures and removes underwater organisms in water taken as the ballast water by keeping a cylindrical filter medium supported by the substrate with one end in the axial direction open and the other end closed, gets, when filtering is to be carried out, an inflow of raw water from the opening to be exhausted out of the filter body by penetrating the filter medium, and gets, when back washing is to be carried out, an inflow of filtrate water from outside of the filter body as the back washing water to be exhausted out of the opening by peeling deposits on the inner face of the filter medium. The substrate 18 has a closing end plate 16, an opening end plate 15 that forms the opening, and a cylindrical and multi-pored substrate 17 that connects the closing end plate with the opening end plate, an
