An isolation resistance measuring apparatus having a fault self-diagnosing function, the apparatus comprising: a first isolation resistance measuring unit and a second isolation resistance measuring unit, wherein the first isolation resistance measuring unit and the second isolation resistance measuring unit are each configured with a first resistor and a second resistor; a first diagnosing unit and a second diagnosing unit, wherein the first diagnosing unit is configured with at least one resistor and the second diagnosing unit is configured with at least one further resistor; a first switch configured to connect the first isolation resistance measuring unit to a cathode terminal of a battery when it is ON to form a first circuit and to disconnect when it is OFF; a second switch configured to connect the second isolation resistance measuring unit to an anode terminal of the battery when it is ON to form a second circuit different from the first circuit and to disconnect when it is OFF; a third switch configured to connect the first diagnosing unit to the anode terminal when it is ON to form a third circuit and to disconnect when it is OFF; a fourth switch configured to connect the second diagnosing unit to the cathode terminal when it is ON to form a fourth circuit different from the third circuit and to disconnect when it is OFF; a voltage detection unit configure to sense a first and a second isolation detection voltages and a first and a second diagnosis detection voltages applied to the first and second isolation resistance measuring units (110, 120); and a control unit configured to output a control signal to the first to fourth switches (SW1-4), and determine whether a fault arises at the isolation resistance measuring apparatus by using the first and second isolation detection voltages and the first and second diagnosis detection voltages, characterized in that the first isolation detection voltage, the second isolation detection voltage, the first diagnosis detection voltage and the second diagnosis detection voltage are detected when the states of the first, second, third and fourth switches are according to the following table I: Table I. Switches First Second Third Fourth first isolation detection voltage ON OFF OFF OFF second isolation detection voltage OFF ON OFF OFF first diagnosis detection voltage ON OFF ON OFF second diagnosis detection voltage OFF ON OFF ON a first isolation resistance measuring unit and a second isolation resistance measuring unit, wherein the first isolation resistance measuring unit and the second isolation resistance measuring unit are each configured with a first resistor and a second resistor; a first diagnosing unit and a second diagnosing unit, wherein the first diagnosing unit is configured with at least one resistor and the second diagnosing unit is configured with at least one further resistor; a first switch configured to connect the first isolation resistance measuring unit to a cathode terminal of a battery when it is ON to form a first circuit and to disconnect when it is OFF; a second switch configured to connect the second isolation resistance measuring unit to an anode terminal of the battery when it is ON to form a second circuit different from the first circuit and to disconnect when it is OFF; a third switch configured to connect the first diagnosing unit to the anode terminal when it is ON to form a third circuit and to disconnect when it is OFF; a fourth switch configured to connect the second diagnosing unit to the cathode terminal when it is ON to form a fourth circuit different from the third circuit and to disconnect when it is OFF; a voltage detection unit configure to sense a first and a second isolation detection voltages and a first and a second diagnosis detection voltages applied to the first and second isolation resistance measuring units (110, 120); and a control unit configured to output a control signal to the first to fourth switches (SW1-4), and determine whether a fault arises at the isolation resistance measuring apparatus by using the first and second isolation detection voltages and the first and second diagnosis detection voltages, characterized in that the first isolation detection voltage, the second isolation detection voltage, the first diagnosis detection voltage and the second diagnosis detection voltage are detected when the states of the first, second, third and fourth switches are according to the following table I: Table I. Switches First Second Third Fourth first isolation detection voltage ON OFF OFF OFF second isolation detection voltage OFF ON OFF OFF first diagnosis detection voltage ON OFF ON OFF second diagnosis detection voltage OFF ON OFF ON