An electric power converter is provided, at low costs and in high efficiency, which also enables voltage conversion to be capable of dealing with sharp load variation, even when input voltage and output current ranges are wide. The converter includes a non-isolated buck-boost converter circuit for outputting a DC voltage by increasing or decreasing a voltage being inputted into the circuit, an isolated converter circuit for outputting a DC voltage to a load by inputting a DC voltage outputted from the non-isolated buck-boost converter circuit, and a control unit for controlling the non-isolated buck-boost converter circuit and the isolated converter circuit, whereby the control unit adjusts using only the non-isolated buck-boost converter circuit, by performing the control of a buck-boost voltage ratio between the voltage inputted thereinto and an output voltage of the isolated converter circuit, so as to make the output voltage coincident with its target value.