A DC/DC converter which may be used as a power supply of high capacity. The DC/DC converter comprises first and second converters having their primary terminals connected in series so as to insure high output power and high breakdwon voltage; a first diode for forming a closed circuit together with a transformer of the first converter and a capacitor of the second converter when a switching element of the first converter is turned "off"; and a second diode for forming a closed circuit together with a transformer of the second converter and a capacitor of the first converter when a switching element of the second converter is turned "off".