There are provided a waveguide plate that is made of metallic plates through which through holes are formed and a pair of resin made substrates (first and second substrates) on which a grounding pattern is formed to cover the through holes. Both the waveguide plate and the substrates are laminated with each other using a conductive adhesive such that the waveguide plate is sandwiched by the substrates, whereby a rectangular waveguide is provided. The first substrate has high frequency circuits such as an oscillator that generates high frequency signals. The high frequency signals generated by the oscillator are supplied to an antenna section that is formed on the second substrate via the rectangular waveguide.