A filter device (1, 401, 501, 601), comprising: a filter (11, 411, 511, 611) comprising a substrate (12, 412, 512, 612) made of a dielectric, a pair of wide walls (221, 222, 321, 322, 4221, 4222, 4321, 4322, 5221, 6221) being constituted by a first conductor layer (13, 413, 513, 613) and a second conductor layer (14, 414, 514, 614), respectively, and covering respective opposite surfaces of the substrate (12, 412, 512, 612), and narrow walls (223, 224, 4223, 4224, 5223, 5224, 6223, 6224) being constituted by post walls which are provided inside the substrate (12, 412, 512, 612); and a first waveguide tube (21, 121, 421, 521, 621) and a second waveguide tube (31, 431) each including a tube wall (22, 32, 122, 422, 432, 522, 622) made of a conductor and being placed along the substrate (12, 412, 512, 612), the filter (11, 411, 511, 611) further comprising: a first columnar conductor (118, 418, 518, 618) passing through a first opening (13a1) which is provided in the first conductor layer (13, 413, 513, 613), the first columnar conductor (118, 418, 518, 618) having one end portion located inside the substrate (12, 412, 512, 612), a second columnar conductor (19, 419) passing through a second opening (13a2) which is provided in the first conductor layer (13, 413, 513, 613) or the second conductor layer (14, 414, 514, 614), the second columnar conductor (19, 419) having one end portion located inside the substrate (12, 412, 512, 612), the first waveguide tube (21, 121, 421, 521, 621) being placed such that the first columnar conductor (18, 118, 418, 518, 618) passes through an opening (22a, 122a) which is provided in the tube wall (22, 122, 422, 522, 622) of the first waveguide tube (21, 121, 421, 521, 621) and such that another end portion of the first columnar conductor (18, 118, 418, 518, 618) is located inside the first waveguide tube (21, 121, 421, 521, 621), the second waveguide tube (31, 431) being placed such that the second columnar conductor (19, 419) passes through an opening which is provided in the tube wall (22, 122, 422, 522, 622) of the second waveguide tube (31, 431) and such that another end portion of the second columnar conductor (19, 419) is located inside the second waveguide tube (31, 431), wherein the filter (11, 411, 511, 611) further comprises one or more partition walls (171, 172, 173) being constituted by post walls provided inside the substrate (12, 412, 512, 612) and dividing a region surrounded by the pair of wide walls (13, 14, 413, 414, 513, 514, 613, 614) and the narrow walls (223, 224, 4223, 4224, 5223, 5224, 6223, 6224) into a plurality of resonators (11a to 11d), the one or more partition walls (171, 172, 173) having respective coupling windows (171a, 172a, 173a). a first columnar conductor (118, 418, 518, 618) passing through a first opening (13a1) which is provided in the first conductor layer (13, 413, 513, 613), the first columnar conductor (118, 418, 518, 618) having one end portion located inside the substrate (12, 412, 512, 612), a second columnar conductor (19, 419) passing through a second opening (13a2) which is provided in the first conductor layer (13, 413, 513, 613) or the second conductor layer (14, 414, 514, 614), the second columnar conductor (19, 419) having one end portion located inside the substrate (12, 412, 512, 612), the first waveguide tube (21, 121, 421, 521, 621) being placed such that the first columnar conductor (18, 118, 418, 518, 618) passes through an opening (22a, 122a) which is provided in the tube wall (22, 122, 422, 522, 622) of the first waveguide tube (21, 121, 421, 521, 621) and such that another end portion of the first columnar conductor (18, 118, 418, 518, 618) is located inside the first waveguide tube (21, 121, 421, 521, 621), the second waveguide tube (31, 431) being placed such that the second columnar conductor (19, 419) passes through an opening which is provided in the tube wall (22, 122, 422, 522, 622) of the second waveguide tube (31, 431) and such that another end portion of the second columnar conductor (19, 419) is located inside the second waveguide tube (31, 431), wherein the filter (11, 411, 511, 611) further comprises one or more partition walls (171, 172, 173) being constituted by post walls provided inside the substrate (12, 412, 512, 612) and dividing a region surrounded by the pair of wide walls (13, 14, 413, 414, 513, 514, 613, 614) and the narrow walls (223, 224, 4223, 4224, 5223, 5224, 6223, 6224) into a plurality of resonators (11a to 11d), the one or more partition walls (171, 172, 173) having respective coupling windows (171a, 172a, 173a).