COLONY MEASURING INSTRUMENT

PURPOSE:To easily perform colony measuring operation by measuring the numbers of foreign bodies and grown colonies on a petri dish at the same time after cultivation, and subtracting the number of foreign bodies which is stored before the cultivation. CONSTITUTION:When the petri dish after the cultivation is measured, the petri dish is put in a colony detection device 1 and measurements in the petri dish are perfomed, first. After the measurements are performed, an arithmetic unit 2 calculates a measurement result. Here, the calculated value obtained by measuring the same petri dish before the cultivation is read out of a storage device 3. Then the arithmetic unit 2 subtracts the calculated value of the measurement result before the cultivation from the calculated value of the measurement result after the cultivation. The subtraction result is outputted by an output device 4. Thus, the inside of the petri dish is measured before the cultivation and the result is subtracted from the measurement result after the cultivation to remove the number of the foreign bodies which are originally mixed in the petri dish.