A filter device, comprising: a first filtration unit that is configured to protrude from an upper surface of a tank toward the inside of the tank; and a second filtration unit provided below the first filtration unit to overlap the first filtration unit in a plan view and having a substantially cylindrical shape, wherein the first filtration unit includes a filter case that is provided with a plurality of opening portions in a side surface and has a bottomed substantially cylindrical shape, a lid member that covers an opening end of an upper portion of the filter case, a filter element that is provided inside the filter case and has a substantially cylindrical shape, and an inflow portion that is configured to allow a fluid to flow into a hollow portion of the filter element and is provided between a bottom surface of the filter case and the filter element in a height direction, and wherein: the lid member is detachably provided on the filter case, the filter element is detachably provided on the filter case via the opening end, the filter element includes a filtration material that has a substantially cylindrical shape, and an inner tube that has substantially the same height as that of the filtration material, is provided inside the filtration material, and has a substantially cylindrical shape, the inner tube includes a first region that is formed with an opening portion substantially on the entire surface and a second region that is not formed with the opening portion, and the second region is provided below the first region to include a lower end of the inner tube. a first filtration unit that is configured to protrude from an upper surface of a tank toward the inside of the tank; and a second filtration unit provided below the first filtration unit to overlap the first filtration unit in a plan view and having a substantially cylindrical shape, wherein the first filtration unit includes a filter case that is provided with a plurality of opening portions in a side surface and has a bottomed substantially cylindrical shape, a lid member that covers an opening end of an upper portion of the filter case, a filter element that is provided inside the filter case and has a substantially cylindrical shape, and an inflow portion that is configured to allow a fluid to flow into a hollow portion of the filter element and is provided between a bottom surface of the filter case and the filter element in a height direction, and wherein: the lid member is detachably provided on the filter case, the filter element is detachably provided on the filter case via the opening end, the filter element includes a filtration material that has a substantially cylindrical shape, and an inner tube that has substantially the same height as that of the filtration material, is provided inside the filtration material, and has a substantially cylindrical shape, the inner tube includes a first region that is formed with an opening portion substantially on the entire surface and a second region that is not formed with the opening portion, and the second region is provided below the first region to include a lower end of the inner tube. the lid member is detachably provided on the filter case, the filter element is detachably provided on the filter case via the opening end, the filter element includes a filtration material that has a substantially cylindrical shape, and an inner tube that has substantially the same height as that of the filtration material, is provided inside the filtration material, and has a substantially cylindrical shape, the inner tube includes a first region that is formed with an opening portion substantially on the entire surface and a second region that is not formed with the opening portion, and the second region is provided below the first region to include a lower end of the inner tube.