A power monitoring apparatus monitors the voltage fluctuation range of an AC
power
supply and the duration of voltage fluctuations within the voltage fluctuation
range. The power monitoring apparatus looks up a power failure rank table for determining
the power failure rank of the power supply on the basis of the voltage fluctuation
range and the duration obtained as the monitoring result to determine the power
failure rank of the power supply. The power monitoring apparatus sends a power
failure signal indicating the power failure rank to a power supply destination
of an AC power supply.
