We report support system for histopathologic diagnosis of hepatocellular carcinoma, and especially for differential diagnosis between normal and extremely well-differentiated hepatocellular carcinoma (EHCC). To extract the positions of hepatocellular nuclei, a three-step method composing candidates extraction, contours extraction and screening steps was proposed. About 83% of the nuclear positions were correctly extracted with 10% of the positions wrongly extracted. As a result, the time required to correct the wrong positions using a graphical user interface (GUI) was reduced. Nuclear density and ratio of high nuclear density area are proposed as the two features calculated using these extracted positions. Simulation results showed the effectiveness of these features for differential diagnosis between normal and EHCC. A GUI was developed that enables a user to extract the nuclear positions, to correct the positions, and to calculate the proposed features by simple button operations. The total time for processing one image and extracting the features was about 2 minutes. This system would be helpful in actual diagnosis.