A power conditioner for supplying controlled power generated from a power source such as a fuel cell or a solar battery to a load. The power conditioner includes a main converter converting the output voltage of the power source; an auxiliary converter converting the output voltage of the main converter to a voltage that is supplied to BOP elements; and a direct connecting line connecting the output voltage of the power source to the auxiliary converter bypassing the main converter. Accordingly, because the voltage for the power to be supplied to the BOP elements is converted only once, the power loss can be significantly reduced compared to the power loss from a conventional power conditioner.