Clinical cytology is an important diagnostic procedure in the early detection of cancer. However, both the scarcity of cytologists and the time-consuming nature of the examination are hindering its application to mass survey. To alleviate this situation, a prototype apparatus was constructed so that the determination of malignancy could be made automatically. A spot of light is thrown upon a specimen. Scanning is performed over 10,000 cell nuclei. Optical density modulated by the nucleus is fed into a computer, which recognizes an individual nucleus as a single nucleus, classifies it into five area-levels, and totals the number of nuclei in each class. All the steps including the mechanical operation are completely automated. Preliminary tests revealed satisfactory results on the preparation made from Ehrlich's ascitic cell tumour. Because the installed computer has other several potentialities for yielding available criteria, the decision-making procedure should finally be worked out by a composite criteria.