In the mass production of dielectric resonator oscillators (DROs), it is necessary to regulate the position where a dielectric resonator is placed with a high degree of accuracy and thus time required for the assembly work increases undesirably. Further, a terminating resistor and earthing means are formed at an end of a transmission line that is electromagnetically coupled to the dielectric resonator and constitutes the resonator on a dielectric substrate, and as a result the production cost increases. The present invention is characterized in that, in the components of a DOR, only a transmission line is formed on a dielectric substrate, and an oscillating active element and a terminating resistor and the earthing means on an MMIC chip are connected to the transmission line with metallic wires, metallic ribbons, or the like. Further, an open stub is formed in the middle of the transmission line on the side close to the oscillating active element when it is viewed from the dielectric resonator.