A control target area determiner 21 sets a rectangular target area surrounding a measurement area specified on an optical microscopic image of a sample. A validity determiner 22 and binarization processor 23 divide all small areas within the target area into a first group which overlaps the measurement area and a second group which does not overlap, and assign valid flag “1” and invalid flag “0” to the first and second groups, respectively. A compression processor 24 reads individual flag data in a predetermined order on all small areas within the target area, creates a binary-data string, and compresses the string by run length encoding. A control-processing unit 2 sends the compressed data to a main apparatus 1 along with other data, including information indicating the position of the first small area within the target area. The main apparatus 1 performs an analysis while gradually decoding those data.