A power supply apparatus including: a converter unit that performs power conversion, an output voltage detection unit that detects an output voltage, an output voltage control unit that performs control for making the output voltage of the power supply apparatus be close to a set voltage in accordance with a comparison result between a detected voltage of an output voltage of the converter unit and a reference voltage, and instructed value reading means for reading an instructed value regarding the output voltage from outside, wherein a voltage is applied across output terminals (+V out, GND) from an external circuit connected to the output terminals (+V out, GND) also during a time when the converter unit stops an operation, characterized in that the power supply apparatus comprising: temporary output voltage setting means configured to set the output voltage at a time when the converter unit starts to operate such that the output voltage becomes identical or approximately identical to (i) a target voltage that is set in advance and that is higher than a pre-bias voltage applied from the external circuit and lower than the instructed value, or (ii) a pre-bias voltage applied from the external circuit, said voltage being detected by the temporary output voltage setting means adapted to use the output voltage detection unit; and steady output voltage setting means configured to set the output voltage such that, after the output voltage became identical or approximately identical to (i) the target voltage or (ii) the pre-bias voltage applied from the external circuit, the output voltage becomes the instructed value; wherein the temporary output voltage set value and the steady output set value of the output voltage are set by controlling the reference voltage; and that the output voltage control unit and the output voltage setting means are configured to operate with a voltage of the output terminal (+V out) of the power supply apparatus as a power supply voltage. a converter unit that performs power conversion, an output voltage detection unit that detects an output voltage, an output voltage control unit that performs control for making the output voltage of the power supply apparatus be close to a set voltage in accordance with a comparison result between a detected voltage of an output voltage of the converter unit and a reference voltage, and instructed value reading means for reading an instructed value regarding the output voltage from outside, wherein a voltage is applied across output terminals (+V out, GND) from an external circuit connected to the output terminals (+V out, GND) also during a time when the converter unit stops an operation, characterized in that the power supply apparatus comprising: temporary output voltage setting means configured to set the output voltage at a time when the converter unit starts to operate such that the output voltage becomes identical or approximately identical to (i) a target voltage that is set in advance and that is higher than a pre-bias voltage applied from the external circuit and lower than the instructed value, or (ii) a pre-bias voltage applied from the external circuit, said voltage being detected by the temporary output voltage setting means adapted to use the output voltage detection unit; and steady output voltage setting means configured to set the output voltage such that, after the output voltage became identical or approximately identical to (i) the target voltage or (ii) the pre-bias voltage applied from the external circuit, the output voltage becomes the instructed value; wherein the temporary output voltage set value and the steady output set value of the output voltage are set by controlling the reference voltage; and that the output voltage control unit and the output voltage setting means are configured to operate with a voltage of the output terminal (+V out) of the power supply apparatus as a power supply voltage. temporary output voltage setting means configured to set the output voltage at a time when the converter unit starts to operate such that the output voltage becomes identical or approximately identical to (i) a target voltage that is set in advance and that is higher than a pre-bias voltage applied from the external circuit and lower than the instructed value, or (ii) a pre-bias voltage applied from the external circuit, said voltage being detected by the temporary output voltage setting means adapted to use the output voltage detection unit; and (i) a target voltage that is set in advance and that is higher than a pre-bias voltage applied from the external circuit and lower than the instructed value, or (ii) a pre-bias voltage applied from the external circuit, said voltage being detected by the temporary output voltage setting means adapted to use the output voltage detection unit; and steady output voltage setting means configured to set the output voltage such that, after the output voltage became identical or approximately identical to (i) the target voltage or (ii) the pre-bias voltage applied from the external circuit, the output voltage becomes the instructed value; wherein the temporary output voltage set value and the steady output set value of the output voltage are set by controlling the reference voltage; and that the output voltage control unit and the output voltage setting means are configured to operate with a voltage of the output terminal (+V out) of the power supply apparatus as a power supply voltage.