As described above, according to the present invention, original data that is input as records is compressed. The compressed data is temporarily stored in the buffer memory and then recorded on the magnetic tape. When data is recorded, it is determined whether or not the buffer memory overflows. When the determined result represents that the buffer memory overflows, the value of the counter is dynamically changed. Thus, the buffer memory can be prevented from overflowing. The compressed data is recorded as entities and recorded to each group. The BAT flag that represents the type of the entity is added. When data is reproduced, it is determined whether the last entity of the current group is an entity that continues to the next group or an entity that is completed in the current group. When the last entity continues to the next group, the next group is accessed. When the last entity is completed in the current group, no further accessing operation is performed. Thus, the reproducing process can be effectively performed.