The present invention has an object to provide a filter device in which a filter is directly fixed to a container, thus eliminating the use of a filter frame. A fuel filter 6 of a fuel supply system 60 includes a filter element 22 for filtering fuel and a filter case 21 made of resin which houses the filter element 22. Ends 22b and 22c of the filter element 22 are directly fixed to an inner wall surface of the filter case 21 by welding. Further, the filter case 21 is formed, on the inner wall surface, with a groove 34 at each end of a weld part 36 in a longitudinal (vertical) direction. The groove 34 serves to receive a melted resin squeezed out from the weld part 36. To isolate the weld part 36 from a (filtering) body 22a of the filter element 22, protrusive ribs 32 and 33 are provided on the inner wall surface of the filter case 21.