A filter device including a filter and waveguide tubes broadens a band in which return loss is small. A filter device (1) includes: a filter (11) including wide walls (13, 14) and narrow walls (16); and first and second waveguide tubes (21, 31). The filter 11 includes first and second columnar conductors (pins 18 and 19) each passing through an opening (13a1 or 13a2) which is provided in the wide wall (conductor layer 13) and having one end portion (181, 191) located inside the substrate (12). The first and second waveguide tubes (21, 31) are placed such that each of the first and second columnar conductors (pin 18, 19) passes through an opening (22a, 23a) and such that another end portion (182, 192) of each of the columnar conductors (pin 18, 19) is located inside the waveguide tube (21, 31).