The present invention provides a combined cycle electric power generating plant that effectively reduces the noise produced by the exhaust of steam in the warm-up process or the like. This plant has a duct which drives the steam used for warming a steam cooling system which cools the high temperature parts which are cooled of the gas turbine at the start of the operation to an exhaust duct of the gas turbine. The steam used for warming a steam cooling system is directed to the exhaust duct of the gas turbine, and the noise which is produced by the exhaust of the steam for warming is silenced by the exhaust duct of the gas turbine.