The invention provides a computer monitoring system for performing monitoring to improve a use efficiency of a monitor-subject computer and also for detecting illegal mail transmission/reception, illegal browsing, etc., which cannot be detected by a prior art, thus promoting proper use of the computers in the network.In this computer monitoring system, a monitor-subject PC2 records a log of a use state of application software products, which log is acquired from the monitor-subject PC2 by a monitor PC1, which in turn calculates a using time and a use rate of each of the application software products except an idle state time and also a time and a use rate of the idle state, thus outputting and displaying the use rate.