A storage device includes a volatile memory, a nonvolatile memory, an auxiliary power source, and a controller configured to start a setting process to store a setting value in the volatile memory in response to a setting command received from a host, and operate in accordance with one or more setting values stored in the volatile memory. When the controller determines that a main power supply will stop, power from the auxiliary power source starts to be primarily used, and the controller saves at least part of said one or more setting values stored in the volatile memory to the nonvolatile memory, before power supply from the auxiliary power source ends.