An apparatus for diagnosing a negative electrode contactor of a battery pack, wherein the battery pack includes a positive electrode contactor provided on a charge-discharge path connected to a positive electrode terminal of the battery pack and the negative electrode contactor provided on a charge-discharge path connected to a negative electrode terminal of the battery pack, the apparatus comprising: a first voltage measuring unit connected between a ground and a first node to which a positive electrode terminal of a battery module included in the battery pack and one end of the positive electrode contactor are commonly connected, wherein the first voltage measuring unit is configured to measure a first measurement voltage applied between the first node and the ground; a second voltage measuring unit connected between the ground and a second node to which a negative electrode terminal of the battery module and one end of the negative electrode contactor are commonly connected, wherein the second voltage measuring unit is configured to measure a second measurement voltage applied between the second node and the ground, characterized by a positive electrode protection capacitor located between the ground and the positive electrode terminal of the battery pack; a negative electrode protection capacitor located between the ground and the negative electrode terminal of the battery pack; and a diagnosing unit having a plurality of diagnosis circuits configured to selectively connect two of the first node, the second node, a third node to which the other end of the positive electrode contactor and one end of the positive electrode protection capacitor are commonly connected, a fourth node to which the other end of the negative electrode contactor and one end of the negative electrode protection capacitor are commonly connected, and the ground, wherein the diagnosing unit is configured to: measure a first diagnosis voltage applied between the third node and the second node, a second diagnosis voltage applied to the positive electrode protection capacitor and a third diagnosis voltage applied to the negative electrode protection capacitor, diagnose whether the battery module is electrically leaked by using the first measurement voltage and the second measurement voltage, and diagnose whether the negative electrode contactor is short-circuited by using at least one of the first diagnosis voltage, the second diagnosis voltage and the third diagnosis voltage. a first voltage measuring unit connected between a ground and a first node to which a positive electrode terminal of a battery module included in the battery pack and one end of the positive electrode contactor are commonly connected, wherein the first voltage measuring unit is configured to measure a first measurement voltage applied between the first node and the ground; a second voltage measuring unit connected between the ground and a second node to which a negative electrode terminal of the battery module and one end of the negative electrode contactor are commonly connected, wherein the second voltage measuring unit is configured to measure a second measurement voltage applied between the second node and the ground, characterized by a positive electrode protection capacitor located between the ground and the positive electrode terminal of the battery pack; a negative electrode protection capacitor located between the ground and the negative electrode terminal of the battery pack; and a diagnosing unit having a plurality of diagnosis circuits configured to selectively connect two of the first node, the second node, a third node to which the other end of the positive electrode contactor and one end of the positive electrode protection capacitor are commonly connected, a fourth node to which the other end of the negative electrode contactor and one end of the negative electrode protection capacitor are commonly connected, and the ground, wherein the diagnosing unit is configured to: measure a first diagnosis voltage applied between the third node and the second node, a second diagnosis voltage applied to the positive electrode protection capacitor and a third diagnosis voltage applied to the negative electrode protection capacitor, diagnose whether the battery module is electrically leaked by using the first measurement voltage and the second measurement voltage, and diagnose whether the negative electrode contactor is short-circuited by using at least one of the first diagnosis voltage, the second diagnosis voltage and the third diagnosis voltage. measure a first diagnosis voltage applied between the third node and the second node, a second diagnosis voltage applied to the positive electrode protection capacitor and a third diagnosis voltage applied to the negative electrode protection capacitor, diagnose whether the battery module is electrically leaked by using the first measurement voltage and the second measurement voltage, and diagnose whether the negative electrode contactor is short-circuited by using at least one of the first diagnosis voltage, the second diagnosis voltage and the third diagnosis voltage.