Abstract: A millimeter-wave device includes a pedestal having an upper surface; a microwave IC chip operating at a millimeter wave band, the chip being mounted on the upper surface of the pedestal; line substrates having respective transmission lines connected to the microwave IC chip, the line substrates being mounted on opposite sides of the microwave IC chip on the upper surface of the pedestal; a lid covering and sealing the microwave IC chip and the line substrates, the lid being disposed opposite the upper surface of the pedestal; and waveguides, each waveguide including a waveguide input/output part having an opening penetrating the pedestal transverse to the upper surface and a waveguide end portion connected to the waveguide input/output part, the waveguides being disposed in the vicinity of opposite ends of the pedestal.