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This paper is concerned with the development of magnetic fluid micro devices. Liquid responses of a magnetic fluid adsorbed on a ring-shaped permanent magnet subject to alternating magnetic fields were investigated. The magnetic fluid adsorbed on the permanent magnet forms a hole, and the diameter of magnetic hole may be changed by external magnetic fields. Frequency characteristics of micro diaphragm mechanism based on the magnetic fluid-permanent magnet element system were examined experimentally. Liquid surface responses of the magnetic fluid were examined over the wide frequency range. It was revealed that the frequency of the liquid surface motion corresponds to the frequency of external alternating magnetic field. The magnetic field distributions around the element system were also measured, and relations between the magnetic field distribution and magnetic fluid surface motion were discussed. Furthermore, the improved model of the magnet-magnetic fluid element was produced, and its driving characteristics were obtained experimentally.