PURPOSE: To deter an excess pressure of feed water confined in a condensate feeding line and an economizer at a hot banking of an exhaust heat recovering boiler.

CONSTITUTION: A protective device of a condensate feeding system of an exhaust heat recovering boiler is equipped with a condensate feeding line CFL connecting a condenate vessel 6 to an economizer 1 incorporated into the exhaust heat recovering boiler HRSG, a minimum flow line MFL divided from an outlet side of a feed water pump 4 of a condensate feeding line and connected to the condensate vessel 6, and a guiding and communicating line 10 with insertion of a by-pass valve 11 onto a pipe line connecting this minimum flow line MFL and the condensate feeding line CFL.