To acquire data for deciding an illumination level simply even by an unskilled adjustment operator.

The data acquisition apparatus is provided with a level change part 1 in which a combination of the illumination level and an iris level is changed into a plurality of levels and in which its change is repeated in the designated number of times, a data acquisition part 2 which acquires image data in the combination of the illumination level and the iris level changed by the part 1 and by which a luminance value calculated by adding and averaging the data in a designated range is stored in a data storage part 3 and a luminance-mean-value calculation part 4 which calculates a luminance mean value at each illumination level stored in the part 3. The combination of the illumination level and the iris level in which e.g. the luminance mean value becomes a value of about 128 in the middle of a luminance range of 0 to 255 is decided as an optimum illumination level and an optimum iris level, and a formation is adjusted.