Inner conductor formation holes having inner conductors formed on the inner walls thereof are formed in a dielectric block. Both of the ends of one of the inner conductors are open and led out as terminal electrodes which function as balanced ports. Both of the ends of another inner conductor are connected to an outer conductor to be grounded, and the center portion of the inner conductor between the ends is led out as a terminal electrode which functions as an unbalanced port. The circuit can also be realized with striplines or microstriplines on a dielectric substrate. Thus, a balanced-unbalanced converter having these terminal electrodes as balanced and unbalanced ports is formed.