A storage device started when connected to a computer so as to be able to communicate. The storage device includes: an interface for controlling communication with the computer, a data storage unit for storing data received from the computer via the interface, a radio signal processing unit for receiving radio signals including ID information at a predetermined timing and for authenticating the received ID information, and a control unit for encrypting data using the authenticated ID information as a key, for sending the encrypted data to a data storage unit, and for disabling communication with the computer via the interface when radio signals including the authenticated ID information are not received by the radio signal processing unit within a predetermined period of time.