In the power supply apparatus which performs voltage conversion of an input voltage (Vbat), with a predetermined set voltage as a target value, and outputs the converted voltage, a boost ratio setting unit sets a boost ratio (XCP) of the charge pump circuit based on the input voltage (Vbat) and a predetermined set voltage. A voltage adjustment unit is a regulator circuit, and adjusts voltage (Vx) so that output voltage (Vout) of the charge pump circuit approaches the set voltage. An output voltage setting unit generates a predetermined set voltage as a digital value (Dset). An A/D converter performs analog-digital conversion of the input voltage (Vbat). The boost ratio setting unit sets the boost ratio based on a result of comparing an input voltage (Ddet) that has undergone analog-digital conversion, and the set voltage (Dset).