A circuit protector includes a plurality of detection lines that connect between a battery pack and a monitoring circuit, an overvoltage protection element connected between the detection lines that keeps the voltage applied to the monitoring circuit at a fixed voltage, and a circuit protection element disposed in each detection line that disconnects an electrical link between the monitoring circuit and the battery pack when a current beyond a predetermined current value flows into the detection line. When the excess voltage occurs in the battery pack, the overvoltage protection element maintains between each detection line in a short circuit state, and the circuit protection element disconnects the electrical link between the battery pack and the monitoring circuit by a short-circuit current that flows between the detection lines via the overvoltage protection element.