A vehicle-mounted emergency report device having a function of transmitting an emergency report signal to a center device via a communication network when a vehicle has been determined to collide, includes a backup battery supplying an operating power when electric power supplied from a vehicle battery decreases, and a voltage detection unit detecting a voltage of the backup battery. Also, the vehicle-mounted emergency report device has a first determination unit determining whether the voltage detected is lower than a battery exhaustion warning threshold, a second determination unit determining whether a second order differential coefficient calculated by differentiating a battery voltage function twice by time is negative, and a warning unit refraining from warning when the voltage detected is lower than the threshold and the coefficient is not negative, and warning when the coefficient is negative. Thus, decrease of a discharge performance of the backup battery can be detected accurately.