An object of the present invention is to provide a battery state monitoring circuit and a battery device which are capable of normally operating when a charger (301) is connected to an opposite polarity in error, and then correctly connected. In the case where the charger (301) is connected to the opposite polarity in error and then correctly connected, a logic circuit (305) does not output a power-down signal that powers down the respective circuits to the respective circuits by the aid of a power-down preventing circuit (110). As a result, the battery device normally operates without falling into the power-down state.