A high-frequency circuit device includes a dielectric member 1, a shielding conductor 2 surrounding the dielectric member 1, a support member 3 for fixing and supporting the dielectric member 1, and a pair of transmission lines 4 each of which is formed of a microstrip-line. Each of the transmission lines includes a substrate 6 formed of a dielectric material, a strip conductor 5, and an earth conductor layer 9. An end portion of the strip conductor 5 faces part of the dielectric member 1 and functions as a coupling probe for input/output coupling. Each of the transmission lines 4 is formed of a strip line, a mictostrip line, a coplanar line or the like, and has low-loss when connected to a circuit board.