A dielectric resonator capable of resonating at a predetermined resonance frequency has a dielectric substrate, a first electrode formed on a first surface of the dielectric substrate and having a first opening, a second electrode formed on a second surface of the dielectric substrate and having a second opening, a first conductor plate disposed by being spaced apart from the dielectric substrate by a predetermined distance, and a second conductor plate disposed by being spaced apart from the dielectric substrate by a predetermined distance. The region of the dielectric substrate defined between the first and second electrodes, a free space defined between the first electrode and the first conductor plate and another free space defined between the second electrode and the second conductor plate are cut-off regions for attenuating a high-frequency signal having the same frequency as the resonance frequency. This dielectric resonator can be used in a millimeter wave band, can resonate with markedly small variations of its resonance frequency even if the temperature thereof varies, and can be manufactured at a low cost.