1. A computer storage tangibly storing a communication performance analyzing program containing instructions for causing a computer to execute an operation including analyzing a communication performance among computers of a computer system formed by connecting a plurality of computers by a network, comprising: acquiring communication time data among the computers of the computer system on a plurality of observation items; executing a communication time combining operation that permutes the communication time data on the plurality of observation items to make communication time combination data; executing a clustering analysis operation that conducts a statistical analysis by clustering the communication time combination data to group the communication time combination data as to combinations of computers or the observation items; displaying the analyzed result; executing a principal component analysis that conducts a statistical analysis on the communication time data by way of principal component analysis, using the communication time combination data prepared by the communication time combining, the clustering analysis groups the results of the statistical analysis conducted by the principal component analysis and displays a scatter diagram based on predetermined principal components, wherein the principal component analysis conducts an analysis on the similarity of the plurality of observation items, using the communication time combination data prepared by the communication time combining, and generates principal component analysis/observation item data; and the clustering analysis conducts a grouping operation for the similarity of the observation items, using the principal component analysis/observation item data generated by the principal component analysis.