1. A cell analyzer comprising: a cytometric device which measures cells that are nuclear stained; a display which displays a histogram of a fluorescence intensity by using a result of the measurement by the cytometric device; and a computer comprising at least one processor configured to obtain a number of strong-area cells that are distributed in an area where the fluorescence intensity is stronger than normal cells, and determine a malignancy grade of cancer using the number of strong-area cells and the histogram.