A storage device includes a controller configured to control the storage device, and a storage area for security information, the security information including flag information indicating whether reading or writing of data from/to the storage device is permitted and time information indicating a cumulative time value during which power of the storage device has been turned on. When a first command is received from a host device, the controller generates encrypted data by encrypting data obtained by combining the time information and the security information, and after transmitting the encrypted data to the host device, shifts the storage device to a low power state.