A resonance device with strengthened coupling between a resonator and a transmission line without reducing an unloaded Q of the resonator. The resonance device includes a micro-strip line as a transmission line, which has a dielectric substrate, a main conductor, and an earth conductor, both of which are formed on the dielectric substrate, and a resonator disposed near the main conductor of the micro-strip line to be electromagnetically coupled thereto. At a part of the main conductor of the micro-strip line where it is coupled to the resonator, an electrodeless portion such as a slit is formed in a direction substantially parallel to a signal-propagating direction.