A comparator circuit includes: a switching element that is disposed between a positive electrode of a battery cell and a fixed potential supply source, that has a control terminal connected to a negative electrode of the battery cell, and that operates in response to a voltage applied from the battery cell to the control terminal; a voltage regulating unit that is disposed between the battery cell and the switching element and that regulates the voltage applied from the battery cell to the switching element; and an output signal line that outputs a potential between the switching element and the fixed potential supply source.