A Switched Reluctance (SR) generator having improved efficiency at low and high speed is disclosed. The SR generator includes a step-up converter for controlling an excitation voltage of an excitation capacitor capable of providing a phase winding with an excitation current. Therefore, the SR generator can control the excitation current, and can provide a phase winding with a sufficient excitation current, thereby improving efficiency. The step-up converter is arranged between a battery capable of storing generated power and the excitation capacitor, boosts a voltage of the battery, and provides the excitation capacitor with the boosted voltage. Therefore, the SR generator does not include an additional power-supply unit for a boosting function, resulting in simplification of an overall structure and reduction of a production cost.