A multiple-output power supply unit comprising: a transformer that includes: a primary winding; and a secondary winding which has a first node and a second node; a rectification diode for rectifying an alternating-current voltage generated at the first node and generating a secondary-side voltage by smoothing the rectified voltage with a capacitor; a first output terminal that is connected to the first node through the rectification diode so as to output a first voltage corresponding to the secondary-side voltage; a first constant voltage element that is connected to the first output terminal; a current limiting resistor that is provided connecting the first constant voltage element to the second node; a second output terminal that is connected at the connection between the first constant voltage element and the current limiting resistor so as to output a second voltage different from the first voltage; a current generation circuit that is provided connecting the first node to ground so as to cause a predetermined current to flow between the first node and the ground by the secondary-side voltage; and a transformer driver circuit that is connected to the primary winding so as to drive the transformer; characterized by: a second constant voltage element, the second constant voltage element being one of a Zener diode, a transistor and a varistor, that is provided connecting the second node to ground; and a secondary-side voltage control circuit that is configured to control the transformer driver circuit so as to generate the secondary-side voltage having a predetermined value at the first node. a transformer that includes: a primary winding; and a secondary winding which has a first node and a second node; a primary winding; and a secondary winding which has a first node and a second node; a rectification diode for rectifying an alternating-current voltage generated at the first node and generating a secondary-side voltage by smoothing the rectified voltage with a capacitor; a first output terminal that is connected to the first node through the rectification diode so as to output a first voltage corresponding to the secondary-side voltage; a first constant voltage element that is connected to the first output terminal; a current limiting resistor that is provided connecting the first constant voltage element to the second node; a second output terminal that is connected at the connection between the first constant voltage element and the current limiting resistor so as to output a second voltage different from the first voltage; a current generation circuit that is provided connecting the first node to ground so as to cause a predetermined current to flow between the first node and the ground by the secondary-side voltage; and a transformer driver circuit that is connected to the primary winding so as to drive the transformer; characterized by: a second constant voltage element, the second constant voltage element being one of a Zener diode, a transistor and a varistor, that is provided connecting the second node to ground; and a secondary-side voltage control circuit that is configured to control the transformer driver circuit so as to generate the secondary-side voltage having a predetermined value at the first node. a second constant voltage element, the second constant voltage element being one of a Zener diode, a transistor and a varistor, that is provided connecting the second node to ground; and a secondary-side voltage control circuit that is configured to control the transformer driver circuit so as to generate the secondary-side voltage having a predetermined value at the first node.