To enable the drive in condition that the input power is made constant regardless of the ripple of a voltage value, by providing an oscillatory motor device with a pulse width changing circuit which changes the pulse width of a pulse signal, according to the power voltage value of a drive circuit.

A microcomputer 11 sends a logic circuit a signal to control the ON time of the FET of each switching circuit 10 and 10', according to the level of the power voltage Vbat inputted from a voltage detection means 12, and it controls the pulse width of the signals A, A' B, and B' from each circuit 10 and 10' so that the pulse width may increase more, the more voltage level drops. That is, when Vbat is high, the pulse width of the switching pulse is set narrow. At this point, the input voltage to a motor becomes smaller as compared with the case when the pulse width is wide, thus this can put it at fixed power value, preventing the overentering of input voltage. Moreover, when the Vbat is low, the pulse width of switching pulse is set wide. This way, the input power to the motor increases, and it can be put to the fixed power value.