A DC/AC converter includes a resonant circuit having a first capacitor connected to at least one of a primary winding and a secondary winding of a transformer and an output end connected to a load, the resonant circuit receiving an alternating signal having a predetermined frequency and amplitude to pass a current, a variable impedance element connected in parallel with a part of the output end of the resonant circuit, the variable impedance element changing the impedance value thereof according to a current passing through the load, and a controller to control the current passing through the load to a predetermined value by changing the resonant frequency of the resonant circuit according to the changed impedance value of the variable impedance element.