To speedily record necessary data by files on a DAT(digital audio tape recorder) tape.

The measuring instrument is equipped with at least an A/D converter which digitizes waveform data, a memory which holds the digital data, a display unit which displays the digital data held in the memory, and a DAT which classifies the digital data held in the memory into file data corresponding to file information for indexes and waveform data and records them on the DAT tape 8 by the files. On the DAT tape 8, the file data of the original file and the file information corresponding to it are recorded in order and then the file data of the currently recorded file up to the final file and file information from the original file to the currently recorded file are recorded as a set repeatedly in the file order to enable speedy recording processing.