A high-frequency module includes a stiffener (a support substrate), a resin base member of which one surface is fixed to the stiffener, a first conductive pattern formed on said one surface of the resin base member, a second conductive pattern formed on the other surface of the resin base member for constituting a waveguide in combination with the first conductive pattern to pass a high-frequency signal through the resin base member and including a window for allowing the high-frequency signal to pass therethrough, a cap for covering a semiconductor element and for absorbing or reflecting the high-frequency signal, an adopter (a waveguide tube) fixed onto the second conductive pattern such that one open end thereof surrounds the window, and an antenna fixed to the other open end of the adaptor.