PURPOSE: To prepare highly reliable quality control data, by starting automatic operation by the measured values except the measured value of extra one time measurement, when the number of measured data becomes the number, which is larger than the desired number to be set at least by one time measurement.

CONSTITUTION: A digital display type length measuring system is constituted by a micrometer 1 as a length measuring means and a data processing device 2 as a data processing means, which sequentially receives the measured value data from the micrometer 1 and obtains the quality control data and the like from the received measured length value data. When the number of the measured data becomes larger than the desired number to be set, i.e., the sampled number, at least by one time measurement, the data processing device 2 starts the automatic operation by the measured values except the measured value of extra one time measurement.