A storage device (1) is provided to store operation data of an electronic device (2) when the electronic device (2) experiences interruption of electric power. The storage device (1) includes a processing module (13) for storing the operation data, a switch module (11) for outputting a charging voltage signal associated with a DC voltage signal, and an energy storage module (12) charged by the charging voltage signal. The energy storage module (12) outputs a determination voltage signal to the processing module (13) in absence of the charging voltage signal. Further, the processing module (13) converts the determination voltage signal into a digital value, and determines whether to read the operation data according to the digital value upon recovery of the electric power from the interruption.