Abstract: This invention relates to an automatic range control method for a compact and portable optical density/dot percentage measuring device which can use a conventional light table as its light source, and which can digitally display a result of measurement. In the method, information obtained from an A/D converter, which converts a measured analog signal to a digital signal, is positively employed for reducing overall measuring time. An A/D conversion is first made at x1 range by a 10 bit A/D converter. The A/D conversion value is compared with predetermined values to determine a gain to be selected and perform further A/D conversion.