An abnormal voltage detection apparatus is provided for an assembled battery including a plurality of battery blocks connected in series to each other. In the abnormal voltage detection apparatus, each of a plurality of signal detectors is provided in each of battery blocks. Each of the signal detectors detects voltage abnormality or normality in each battery block based on a voltage of each battery block, generates an abnormality detecting signal containing information about the detected voltage abnormality or normality, and outputs the abnormality detecting signal. A signal generator generates an abnormality detecting information signal containing information about whether or not any of the battery blocks in the voltage abnormality is present based on the abnormality detecting signals. A transmission device has an input terminal pair and an output terminal pair which are electrically insulated from each other, and transmits the abnormality detecting information signal to an external apparatus.