An oscillator comprising a dielectric resonator (DR) has a high controllability and reproducibility of coupling between the dielectric resonator (DR) and an oscillation circuit, and an integrated circuit is reduced in size. The dielectric resonator (DR) (1) is composed of a dielectric substrate (2), grounding conductive layers (3a, 3b) formed on both sides of the dielectric substrate (2), and via holes (4a) for electrical connection between the conductive layers. A coupling element (7a) composed of a slot (5a) provided in the central portion of the grounding conductive layer (3a) and a patch (6a) surrounded by the slot (5a) is coupled to the dielectric resonator (DR) (1). The patch (6a) is connected to a transmission line (13a) on an oscillation circuit (9) through a bump (8). The transmission line (13a) is connected to the ground through a termination resistor (15a). On the oscillation circuit MMIC (9), the transmission line (13a) is connected to the gate of a transistor FET (14) A capacitive transmission line (13a) for positive feedback is connected to the transistor FET (14). The output of the transistor FET (14) is connected to a transmission line (13c) for output through a matching circuit (16). The transmission line (13c) is bump-connected to a coplanar line (12a) composed of a signal conductive layer (11a) formed on an edge of the dielectric resonator (DR) (1) and the grounding conductive layer (3a).