Battery information is transmitted from a recording and playback apparatus to a host computer. In the host computer, based on the time for which operation can be continued, corresponding to the current operating status and the remaining battery level that is included in stored battery information, a warning is output, the data of a cache memory is written, data writing prohibition is set, and a forced closing process is performed. With this construction, in a system formed of a portable recording and playback apparatus and a personal computer, a proper system operation corresponding to the remaining battery level of the recording and playback apparatus is obtained, and the data recorded in the recording medium is prevented from being destroyed as a result of operation stopping due to, for example, the remaining battery level becoming zero while recording.