Provided are a front impurity-removing device with a compressor for compression of the exhaust gas from an oxyfuel combustion device to make impurities in the exhaust gas water-soluble and with a cooler for cooling of the exhaust gas compressed by the compressor to condense moisture in the exhaust gas to discharge drainage with the impurities dissolved, and at least a single rear impurity-removing device with a rear compressor for compression of the exhaust gas to a pressure higher than that of the compressor and a rear cooler to discharge drainage. A water sprayer for humidifying the exhaust gas from the oxyfuel combustion device and a front cooler are provided for producing and discharging drainage with impurities dissolved therein upstream of the compressor in the front impurity-removing device.