Disclosed is an isolation resistance measuring apparatus having a fault self-diagnosing function and a fault self-diagnosing method using the same. The isolation resistance measuring apparatus having a fault self-diagnosing function detects whether a fault arises at the isolation resistance measuring apparatus by using first and second isolation detection voltages detected in a state where a diagnosing unit is not connected (an isolation resistance measuring mode) and first and second diagnosis detection voltages detected in a state where the diagnosing unit is connected (a fault self-diagnosing mode). By doing so, it is possible to self-diagnose a fault by using an original function of the isolation resistance measuring apparatus which may measure an isolation resistance.