A method of measuring a magnetic field using a vibrating coil fixed on an ultrasonic vibrator is proposed. By measuring the field of the coreless excitation coil, the validity of the mechanism of this magnetic field detection method was confirmed. As a result, the linearity of the output signal to the ultrasonic vibration, coil turns and magnetic field was confirmed. In addition it was confirmed that the resolving power of the method was over 1/10 of the geomagnetism.