Circuit Diagnosing Apparatus and Battery Pack Including the Same

A circuit diagnosing apparatus according to an embodiment of the present disclosure diagnoses a circuit state of a battery pack including a battery cell and a main relay connected in series, and includes: a control unit configured to output a first signal having a preset duty cycle through a first line connected to the main relay according to a predetermined output frequency; and a DC-DC converter further connected to the first line to receive the first signal through the first line and configured to receive a second signal output from the battery cell whenever an operation state of the main relay is shifted to a turn-on state by the first signal, convert the first signal and the second signal, and transmit a first conversion signal and a second conversion signal obtained by the conversion to the control unit.