The aim of the invention is to provide a cavity resonator that has a great variable frequency area of a resonance frequency and is provided with good quality. Such a cavity resonator is provided with a round cross-section. The H11n in wave mode acting as the resonance wave mode exists in said resonator which is separated into two components with regard to the cross-sectional plane (5) thereof. The two cavity components (1, 2) can be displaced against each other in the direction of the common longitudinal axis (7) thereof.