A composite microwave circuit module assembly (80) has a dielectric substrate (20) which is formed by a lower layer, an intermediate layer and an upper layer. The lower layer and the upper layer include a lower ground surface (40) and an upper ground surface (43), respectively, and the intermediate layer includes a radio frequency signal circuit formed by an active circuit element and a passive circuit element. A number of via-holes (50) filled with metal are arranged along the radio frequency signal circuit to short-circuit the upper ground surface (43) and the lower ground surface (40) so as to shield the radio frequency signal circuit. An element mounting cavity (60) is disposed on the intermediate layer with a portion of dielectric above the intermediate layer being removed, and the active circuit element is mounted on an element mounting land in the cavity. The cavity is covered by a conductor plate member (33). A connection terminal (91) connected with the radio frequency signal circuit is provided in a surface of the dielectric substrate without projecting from the surface thereof and allows external electrical connection thereat from outside by a microwave circuit connection structure (81) having a contact member resiliently urged to said connection terminal.