Abstract: A capacitor charger is provided that can control charging voltage with high accuracy, and repeat a process of increasing it to a target charging voltage at high speed. In a first step, an ac voltage is generated in a resonant type inverter section by fixed frequency driving pulses, the ac voltage is converted to a dc voltage, a load capacitor is charged by the dc voltage, a calculation pulse in the driving pulse has a predetermined, fixed driving pulse width, and the load capacitor is charged by &Dgr;Vn each pulse. In a second step, when the charging voltage V1 of the load capacitor and the target voltage V2 satisfy an inequality relationship “V2>V1>V2−&Dgr;Vn”, charging is performed by a single or a plurality of final pulses having a driving pulse width W2 (W1>W2) as required to step up the voltage by “V2−V1”.