Embodiments of the invention prevent a storage from being continuously used in a state in which the time of a built-in clock is different from the actual time because of replacement of a battery or intentional tampering of time. In one embodiment, a storage having a recording medium for storing content data includes: a clock that can refer to present time and can set time to reliable standard time on the outside (time synchronization); a built-in power supply that supplies power to the clock; and a nonvolatile memory that records time when the time synchronization for the clock is performed. The storage compares, according to circumstances, the present time indicated by the built-in clock and the time when the time synchronization is performed last time and, when it is made clear that the time synchronization is not performed for time longer than a fixed time set in advance, prohibits an access to a limited access area of the recording medium.