Patent ID: 7716509

Claim:
A storage, comprising: a recording medium; a built-in power supply; a clock that can operate with power from the built-in power supply or an external power supply and set time to standard time; a nonvolatile memory that stores time when the clock sets time; and a subtracter that outputs time, which has elapsed since time setting was performed last, on the basis of the time setting time stored in the nonvolatile memory and time information obtained from the clock, wherein when the output of the subtracter exceeds a predetermined fixed time, the storage blocks an entire recording area or a part of the recording area of the recording medium against a readout request from an apparatus on outside; wherein a threshold value smaller than the fixed time is further set in advance and, when the output of the subtracter is between the threshold value and the fixed time, the storage warns the apparatus on the outside that time setting for the clock is necessary.