A ballast water treatment apparatus includes a filter that is cylindrically formed so as to surround an axis, a case that includes an outer cylindrical portion that is disposed so as to surround the filter, a rotation mechanism that rotates the filter around the axis, an untreated water nozzle that ejects untreated water to a filter-surrounding region that is defined by an outer peripheral surface of the filter and the outer cylindrical portion, a cleaning water nozzle that ejects cleaning water toward the outer peripheral surface of the filter, a filtered water channel through which filtered water that has passed through the filter flows from a region inside the filter to outside of the case, and a discharge channel through which discharged water that has not passed through the filter is discharged from the filter-surrounding region to outside of the case.