To provide the high frequency motion, the minute stroke and force without frictional loss by fixing a reciprocal transmission member to a supporting body through at least two horizontally oscillating arm elements arranged with interval therebetween.

An actuator element comprises, for example, a transmission member 1 in the mode of a connecting rod, and the transmission member 1 is fixed to a supporting body 4 through horizontally oscillating arms 2, 3. The transmission member 1 is reciprocated by applying the force F to one end 5 in the longitudinally axial direction, and the other end 7 works on a final control element 8, for example, a valve. Thus, in the structural mode under the application of the force F, the transmission member 1 can be reciprocated in the longitudinal axial direction. Because the transmission member 1 is moved on the circular orbit in the maximum stroke, an appropriate horizontal motion can be obtained in the longitudinally axial direction. When the stroke is small, the circular motion becomes extremely small, the system works not only without friction but also without substantial loss.