An operation monitoring unit 11 for acquiring process data from sensors 10 installed to a gas turbine and operation information of the gas turbine; communication units 12, 14 for transmitting each of said two kinds of data on the gas turbine acquired in the operation monitoring unit 11; an analysis server 16 which calculates values of equivalent operating time using each of the two kinds of data obtained through the communication units 12, 14, the value of equivalent operating time evaluating a degree of damage of a diagnosed position for each of a plurality of degradation-and-damage modes, and calculates a value of whole equivalent operating time by adding the values of equivalent operating time for the individual degradation-and-damage modes; and a facility management unit 15 client-server systemized using the analysis server 16 and a WWW browser 20 or WWW server 19 are provided. By acquiring the above-described two kinds of data relating to the gas turbine during operating the gas turbine into the analysis server 16 through the communication units 12, 14, a highly accurate analysis result of damage condition can be speedy obtained from values of equivalent operating time for a plurality of degradation-and-damage modes. Further, it is also possible to provide convenience that a person in a remote site can speedy and easily view the analysis results using the WWW browser 20 through the client server system.