A pressurized internal circulating fluidized-bed boiler is incorporated in a combined-cycle electric generating system in which a fuel such as coal, petro coke or the like is combusted in a pressurized fluidized bed and an exhaust gas produced by the combusted fuel is introduced into a gas turbine. The pressurized internal circulating fluidized-bed boiler includes a pressure vessel, a combustor disposed in the pressure vessel and a main fluidized bed combustion chamber provided with an air diffusion device. A thermal energy recovery chamber is partitioned from the main combustion chamber by an inclined partition wall. A fluidized medium flows into and out of the main combustion chamber and the thermal energy recovery chamber. A free board is provided integrally above the main combustion chamber and the thermal energy recovery chamber so that combustion gas from the main combustion chamber and the thermal energy recovery chamber is mixed in the free board.