An apparatus for charging an emergency battery, which provides an emergency power to an emergency core cooling apparatus including an electric pump or a steam pump includes a thermoelectric generation device configured to detect a decay heat and a residual heat produced in a nuclear power plant and configured to convert the detected heat to an electric energy; an electric energy conversion unit connected to the thermoelectric generation device to output a current generated in the thermoelectric generation device as a constant voltage; and the emergency battery configured to store a power outputted from the electric energy conversion unit.