PROBLEM TO BE SOLVED: To provide a filter device capable of improving the filter treatment capacity, and to provide a filtration method using the filter device and a manufacturing method of a filtration fluid using the filter device.SOLUTION: In a filter device, cylindrical filter cartridges 2 are housed in a shell 3. The filter device includes: a division plate 11 which divides the shell 3 into the first outlet/inlet port 3a side and the second outlet/inlet port 3b side; support cylinder bodies 12 which fit in through holes 11a of the division plate 11 and allow inner passages Rb of the filter cartridges 2 at the first outlet/inlet port 3a side to communicate with the second outlet/inlet port 3b side; and post members 13 which are supported by the support cylinder bodies 12 and extend along the inner passages Rb. Each support cylinder body 12 includes: an inner cylinder part 16 to which the post member 13 is inserted and forming a main flow passage Rm in which a fluid flows; an outer cylinder part 17 forming
