The present invention provides a technique for a power supply, and particularly, a buck-boost DC-DC converter which is advantageous for energy harvesting from a low voltage. An LC resonant unit generates a pair of clock type signals having phases opposite to each other from an input signal. These signals are supplied to the clock input terminals of the Dickson charge pumps connected in series and converted into power signals having an amplified voltage so as to match the rated input specification of the buck-boost DC-DC converter of a post-stage.