An AC-DC converter includes a rectifier DB for rectifying an alternating current supplied from an alternating power source AC, a power factor controller 11 connected to an output side of the rectifier DB to improve a power factor, a DC-DC converter 12 that converts a voltage outputted from the power factor controller 11 to another voltage and also outputs either a power or a current limited to a predetermined value, a capacitor for storing an energy and a two-way converter 13 having one input/output terminals connected to output terminals of the DC-DC converter 12 and the other input/output terminals connected to the capacitor to carry out a two-way power conversion.