According to one embodiment, a storage device includes a first nonvolatile memory, a second volatile memory, and a controller. In the second volatile memory, at least one of management information for managing user data written in the first nonvolatile memory and the user data is temporarily written as cache data. The controller is configured to execute processing for writing the cache data written in the second volatile memory to a third memory of the host device, if the storage device is changed from a regular mode to a low power consumption mode in which supplying of power to the second volatile memory is stopped, in response to a request from a host device.