PROBLEM TO BE SOLVED: To accurately diagnose a leakage occurrence state of cooling water of a power generation plant, and report treatment according to the leakage occurrence state.SOLUTION: A power generation plant (1) that condenses steam discharged from a steam turbine (5) in a condenser (7) with cooling water and supplies the condensate to a boiler (4) includes: an acid conductivity meter (A) which measures acid conductivity in the water supplied to the boiler; a degassing type acid conductivity meter (C) which measures acid conductivity after gas components are removed from the water supplied to the boiler; and a control device (2) which diagnoses occurrence of leakage of the cooling water from a combination of measurement results of the acid conductivity meter and degassing type acid conductivity meter, and gives notice of measures corresponding to the diagnosis result.
