To provide a technique of writing data efficiently on a storage medium and thereby play back a content continuously. Specifically, the file allocation table (FAT) of a storage medium is supposed to be read on a partial FAT basis and data is written by a preferred method for that reading method.A data processor writes a content data stream on a storage medium, on which a data storage location is defined based on a file allocation table (FAT). The processor includes: a control section for determining the amount of data to be read continuously until a portion of the data stream, which should be played back during a data stream reading suspended period, is acquired, the suspended period including at least a time for reading a partial FAT forming a part of the FAT; an area detecting section for detecting an available area, in which that amount of data is storable, from a partial area managed by a single partial FAT; and a writing section for writing the content data stream on the available area, whereby the data stream is readable, and the content is playable, based on the partial FAT.