A system for diagnosing the state of a gas turbine; a running monitor device; for capturing the process information coming from a sensor; mounted on the gas turbine of a gas turbine electric power plant; and the running information of the gas turbine; communication devices; for communicating the individual pieces of information of the gas turbine captured by the running monitor device; an analysis server; for calculating a total equivalent running time by calculating the individual equivalent running times for individual deterioration damage modes from the individual pieces of information obtained through the communication devices; and by adding the individual equivalent running times; and a plant administering device; turned into a client server system by using the analysis server; and a WWW browser; or a WWW server; it is possible to provide conveniences that the quick and highly precise analysis result of the damage state can be obtained from the equivalent running times in the deterioration damage modes by introducing the individual pieces of information on the gas turbine during the running of the gas turbine through the communication devices; and that a person at a remote place can read the analysis result quickly and easily with the WWW browser; through the client server system.