A medium storage apparatus writes data for stream type commands on a medium, and improves the reliability of the write data while maintaining the execution time of the commands. The apparatus has a buffer for storing the write data of the write stream type commands, a controller for sequentially writing the data of the buffer to the medium by a head, and a processing unit for skipping the writing of erred sectors for continuing the processing which normally ends if an error occurs, and writing the data to the skipped sector after command execution. By this, the error is corrected such that the medium is correctly read in the next and later read processing, while maintaining the write time specified by the command.