An apparatus for diagnosing a communication fault in a battery pack, comprising: a first slave module connected to first to third communication lines (L1, L2, L3), and configured to receive a synchronization signal from a master module through the first communication line, receive a first output signal from the master module through the second communication line, and transmit an input signal to the master module through the third communication line; a second slave module connected to each of the first communication line, the second communication line and the third communication line in parallel with the first slave module, and configured to transmit a comparison signal to the master module through the third communication line when the second slave module receives a second output signal through the second communication line; and a master module configured to transmit the synchronization signal to the first slave module and the second slave module through the first communication line, transmit the second output signal to the second slave module through the second communication line, and diagnose whether a communication fault has occurred by comparing the input signal with the comparison signal; wherein the first slave module is configured to generate the input signal corresponding to the first output signal and transmit the input signal to the master module when the first slave module receives the first output signal, and the second slave module is configured to generate the comparison signal corresponding to the second output signal and transmit the comparison signal to the master module when the second slave module receives the second output signal; wherein the first slave module and the second slave module are configured to sequentially transmit the input signal and the comparison signal respectively in response to the synchronization signal. a first slave module connected to first to third communication lines (L1, L2, L3), and configured to receive a synchronization signal from a master module through the first communication line, receive a first output signal from the master module through the second communication line, and transmit an input signal to the master module through the third communication line; a second slave module connected to each of the first communication line, the second communication line and the third communication line in parallel with the first slave module, and configured to transmit a comparison signal to the master module through the third communication line when the second slave module receives a second output signal through the second communication line; and a master module configured to transmit the synchronization signal to the first slave module and the second slave module through the first communication line, transmit the second output signal to the second slave module through the second communication line, and diagnose whether a communication fault has occurred by comparing the input signal with the comparison signal; wherein the first slave module is configured to generate the input signal corresponding to the first output signal and transmit the input signal to the master module when the first slave module receives the first output signal, and the second slave module is configured to generate the comparison signal corresponding to the second output signal and transmit the comparison signal to the master module when the second slave module receives the second output signal; wherein the first slave module and the second slave module are configured to sequentially transmit the input signal and the comparison signal respectively in response to the synchronization signal.