Apparatus for recording data, method for recording data and television program receiver

By using program information, the amount of which to be transmitted is not fixed, and related information which is related to the expected amount of the main information, an area for recording main information is ensured in advance on a recording medium. This ensures a reliable recording of a program, the recording of which has already been reserved, without affecting any program which has already been recorded. In addition, even when a change occurs in related information before or after the start of recording information on the recording medium, an area assigned before the start of the recording can be changed corresponding to related information after the change.