A method of displaying gene data assists in discovering expression patterns specific to gene functions and inferring the function of a gene of which the function is unknown. A threshold value representing the degree of similarity of expression patterns is established in advance, and genes having the same function and genes with similar expression patterns to them are extracted and displayed. Cluster analysis is performed on the extracted genes by re-selecting the experiment patterns for clustering. Calculations are performed to see how many functions the genes belonging to a subtree have, and the proportion of each function in the subtree is determined. If a proportion exceeds a predetermined threshold value, they are regarded as a cluster (collection of genes with similar functions) and extracted.