The constant voltage supplying circuit for a circuit breaker according the invention comprises: a first switching device; a constant current source configured to supply a constant current; a feedback circuit section commonly connected to an output terminal of each of the first switching device and the constant current source; a constant voltage source connected to the feedback circuit section, and configured to supply a constant voltage; a current adjusting circuit section connected to the output terminal of the first switching device, and configured to adjust an output current of the first switching device; and a divided voltage resistor section including a first resistor and a second resistor, and configured to provide a divided voltage of an output voltage of the constant voltage supplying circuit, to the feedback circuit section, through a connection node between the first resistor and the second resistor.