A voltage converter with which energy conversion efficiency can be improved during not only low-load conditions but also high-load conditions. A step-down DC-DC converter includes a tapped inductor and a capacitor. The inductor and the capacitor form an LC filter. The inductor and a switching element form a variable inductor having a changeable inductance value. The capacitor and a variable DC voltage source form a variable capacitor having a changeable capacitance value. A control unit changes the inductance value of the variable inductor in accordance with an input/output voltage ratio Vin/Vout between a DC input voltage and a DC output voltage. The control unit changes the capacitance value of the variable capacitor to a capacitance value with which an LC resonant frequency is maintained constant when changing the inductance value of the variable inductor.