A charge monitoring device has a switch which is interposed between a load part having a storage battery and an external AC power source supplying current to the load part through lines and disconnects current supply from the external AC power source to the load part, a current detection circuit which outputs a detection signal according to the difference between levels of current flowing throughthe respective lines, a suppression circuit which suppresses DC components included in the detection signal, a filter circuit which filters frequency components included in the detection signal so asto increase attenuation with improvement of a frequency, a rectifying and smoothing circuit which rectifies and smoothes an output signal obtained by making the detection signal pass through the filter circuit and the suppression circuit, and a short circuit judgment circuit which disconnects the switch by detecting a short circuit when the level of a signal smoothed by the rectifying and smoothing circuit exceeds a reference level set in advance.