A converter includes a rectifying circuit of an AC voltage of an AC power source into a rectified voltage, an input smoothing capacitor Ci, a first series circuit connected to the input smoothing capacitor and including a first and a second switching elements, a second series circuit connected to a connection point of the first and second switching elements and a first end of the input smoothing capacitor and including a primary winding of a transformer and a first capacitor Cri, a controller to alternately turn on/off the first and second switching elements, a rectifying-smoothing circuit (D1, Co) to rectify and smooth a high-frequency voltage of a secondary winding of the transformer into a DC output voltage, and a second capacitor connected between a connection point of the primary winding of the transformer and the first capacitor and a first end of the AC power source.