PURPOSE: To reduce an error of detecting a rotation angle so as to equalize a vibrating amplitude in a stator by independently varying at least one amplitude of electric signals to be input to vibrators of the stator from other amplitudes by an amplitude regulator.

CONSTITUTION: A first DC signal 2-a and a second DC signal 2-b are turned ON, OFF in a vibrating manner in a switching circuit 2-2 to respectively become signals 2-c, 2-d and signals 2-e, 2-f. When it flows to the primary side of a switching transistor 2-3, electric signal group 1-d having a higher voltage than that at the primary side, an equal frequency and a different phase are generated at the secondary side of the transformer. The phase difference of the group 1-d is necessary to excite a traveling wave for a stator 1-3, being 90 degrees. The voltages of the signals 2-a, 2-b are regulated to thereby independently regulate the amplitude of the group 1-d having vibrating properties to be generated at the secondary side of a switching transformer 2-3.