A terminal protection voltage detector circuit is provided for protecting a terminal block having output terminals in a power supply apparatus. A current detector detects output currents flowing from the power supply apparatus to loads via output terminals, and a first comparator configured to compare a sum of the detected output currents with a predetermined first threshold and output a first comparison result signal when the sum of output currents is larger than or equal to the first threshold. A second comparator configured to compare a maximum value of detected output currents with a predetermined second threshold and output a second comparison result signal when the maximum value is equal to or larger than the second threshold. A current stop circuit stops a current from flowing from the power supply apparatus to the output terminals based on the first or second comparison result signal.