A colony counting apparatus includes a reading unit with a visual sensor incorporated therein. The presence of a colony is detected at the end of that colony by moving the reading unit along lines selected at an appropriate pitch and by reading data on the individual points set along each line as logical high or low signals. The values obtained in the above-described counting operation are added and stored in an addition/storage device in a CPU, and the results of addition which are stored in the addition/storage device are output to a suitable display by an outputting device when the counting operation is completed.
