A storage device includes a volatile memory, an auxiliary power source, a nonvolatile memory, a write module, and an inhibition module. The volatile memory stores user data. The auxiliary power source supplies power to the volatile memory when power from a main power source is cut off. The nonvolatile memory is written with the user data, write incomplete information indicating the user data, and power off information indicating that power from the main power source is cut off. While supplied with power from the auxiliary power source when power from the main power source is cut off, the write module writes the write incomplete information, the user data, and the power off information to the nonvolatile memory. The inhibition module inhibits reading of the user data if the power off information is not written in the nonvolatile memory when the volatile memory is supplied with power.