A novel information processing apparatus maintains file system information in a secondary storage device during power saving mode. The information processing apparatus keeps storing file information and mounting information in the secondary storage device without releasing it in shutdown process 303 when it transitions to power saving mode, and uses the saved file information 401 and mounting information 402 in reinitializing process 304 when it returns from power saving mode. User program 201 does not need to execute file initializing process. Also, since mounting information 402 is kept, the information processing apparatus can access the file system in the secondary storage device immediately if the power of the secondary storage device is on and the secondary storage device is available.