An emergency reporting apparatus includes a power supply circuit, a control circuit, and a timer. The power supply circuit generates operating power of the emergency reporting apparatus from a vehicle battery in a vehicle battery mode and from an auxiliary battery in an auxiliary battery mode. The control circuit causes the power supply circuit to switch from the vehicle battery mode to the auxiliary battery mode in response to a trigger event and starts an emergency reporting procedure using the auxiliary battery. The timer measures time elapsed since the power supply circuit switches to the auxiliary battery mode. The control circuit causes the power supply circuit to switch back to the vehicle battery mode, when the elapsed time exceeds a predetermined threshold time period.