Abstract: An APU for an emergency light in case of a fire or power failure includes: a regular power input unit; an emergency power input unit; a changeover switch configured to switch the power input such that the emergency light is automatically turned on by the emergency power in case of a power failure of the regular power; a firefighting power monitoring relay operated by firefighting power when a fire occurs; a firefighting-power-monitoring-relay contact switch configured to connect power from an ATS to the emergency power input unit in connection with the firefighting power monitoring relay; a fire driving unit operated by the power inputted to the emergency power input unit; and an emergency light auto lighting switch configured to connect the emergency light to the regular power input unit, such that the emergency light is automatically turned on.