To provide an oxyfuel combustion boiler system capable of stable operation by preventing water condensation of exhaust gas in an exhaust gas circulation system to eliminate problems caused by condensed water.

An oxyfuel combustion boiler system comprises: a dust collecting apparatus 5 that collects dust and soot in exhaust gas discharged from a boiler 1; a wet desulfurization apparatus 7 that removes sulphur oxide in exhaust gas discharged from the dust collecting apparatus; an exhaust gas circulation system that receives exhaust gas from an exhaust gas intake port 20 disposed on an exhaust gas duct on the outlet side of the dust collecting apparatus or the wet desulfurization apparatus, and circulates the exhaust gas as a part of gas for combustion in the boiler; an air separation apparatus 30 that supplies oxygen-rich gas. In the oxyfuel combustion boiler system, the gas for combustion is generated by mixing the exhaust gas circulated by the exhaust gas circulation system with the oxygen-rich gas supplied from the air separation apparatus. An exhaust gas cooling apparatus 22, which cools at least the exhaust gas received in the exhaust gas circulation system by gas-liquid contact, is included in the oxyfuel combustion boiler system.