This invention is about the power transformer easy to compose a circuit and make stable power by minimizing the output variation resulting in a component error. This comprises a generation/regulation circuit section of switching frequency (20); a maintenance means of the effectine value of FET bias voltage; a bridge circuit (BD3) provided by the control voltage; a load operating circuit (30) including a bias circuit; a regularity frequency generation circuit (50) having multiple timing circuits for switching; the switching output circuit (70) formed by switching transistor; a excessine load detecting part (40) composed of voltage comparator; and a failure display part (90) composed of one stable multivibrator.
