In a protection circuit, a signal line group includes a plurality of voltage signal lines, and the voltage signal lines are connected to electrode portions of a plurality of unit batteries or electrode portions of a battery module. A first protection circuit portion includes a plurality of Zener diodes, and the Zener diodes are connected in parallel to the unit batteries between the plurality of voltage signal lines. A resistor portion group includes a plurality of resistor portions, and the resistor portions are interposed between the Zener diodes and the unit batteries on the voltage signal lines and restrict a current. A second protection circuit portion includes a plurality of varistors, and the varistors are connected in parallel to the unit batteries between the plurality of voltage signal lines.