This paper proposed DC-DC converter for fuel cell that have high voltage and high current output characteristics. It is required step-up converter to use by general power supply, because the general rated voltage of fuel cell is low about 20$sim$50V. The miniaturization of converter and DC link voltage can be controlled and high quality of output voltage uses mainly DC-DC converter. The boost converter and buck-boost converter do not get high boosting ratio. It is that proposed boost-flyback converter. Through simulation and an experiment, it could get high boosting ratio and efficiency more than 90%.