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 (A1) that is formed with an opening portion substantially on the entire surface and a second region (A2) that is not formed with the opening portion, and the second region (A2) 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 (A1) that is formed with an opening portion substantially on the entire surface and a second region (A2) that is not formed with the opening portion, and the second region (A2) 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 (A1) that is formed with an opening portion substantially on the entire surface and a second region (A2) that is not formed with the opening portion, and the second region (A2) is provided below the first region to include a lower end of the inner tube . <EOS>