Provided are corrosive environment monitoring systems and methods whereby corrosive factors are measured in a steam turbine and a corrosive environment is correctly monitored. A corrosive environment monitoring system measures corrosive factors having a part in damaging and deteriorating structural members in a steam turbine and is configured in such a way that steam in the steam turbine is permitted to flow into the corrosive environment monitoring system. Furthermore, in the steam turbine, a condensing mechanism condenses steam that has flowed in and a corrosive factor measuring device is equipped with corrosive factor sensors that measure corrosive factors in condensed water generated by the condensing mechanism.