A waste heat power generation system of a cement calcination plant includes: an AQC boiler having an economizer, an evaporator and a superheater; and a PH boiler having a first evaporator and a superheater. The PH boiler, in addition to the evaporator and the superheater, has a second evaporator on a PH exhaust gas exit side, and a returned hot water from a flasher is introduced into the second evaporator via a steam drum. A hot water heated by the second evaporator is introduced into the steam drum, and a steam from the steam drum is introduced into the low-pressure stage of the steam turbine.