An exhaust gas control system for an internal combustion engine that includes a filter that traps particulate matter contained in exhaust gas emitted from the internal combustion engine, characterized by comprising: differential pressure detecting means for detecting a filter differential pressure that is a difference in pressure, obtained by subtracting a pressure downstream of the filter from a pressure upstream of the filter; deposition amount estimating means for estimating an amount of deposition of particulate matter trapped in the filter on the basis of the filter differential pressure; excessive deposition determination means for determining that the amount of deposition of particulate matter trapped in the filter is abnormal when the amount of deposition of particulate matter, estimated by the deposition amount estimating means, is larger than or equal to a preset excessive deposition determination value; abnormality processing means for announcing an alarm and stopping injection of fuel from adding injectors when the excessive deposition determination means determines the amount of deposition is abnormal; vaporization determination means for determining whether moisture absorbed in the filter has vaporized; prohibiting means for prohibiting the deposition amount estimating means from estimating the amount of deposition of particulate matter when the vaporization determination means determines that moisture absorbed in the filter has not vaporized yet; and emission amount accumulation means for calculating an amount of emission of particulate matter from the internal combustion engine and calculating an accumulated amount of emission by accumulating the calculated amount of emission, wherein when the prohibiting means prohibits the deposition amount estimating means from estimating the amount of deposition of particulate matter, the excessive deposition determination means determines whether the amount of deposition of particulate matter trapped in the filter is abnormal on the basis of the accumulated amount of emission, calculated by the emission amount accumulation means. differential pressure detecting means for detecting a filter differential pressure that is a difference in pressure, obtained by subtracting a pressure downstream of the filter from a pressure upstream of the filter; deposition amount estimating means for estimating an amount of deposition of particulate matter trapped in the filter on the basis of the filter differential pressure; excessive deposition determination means for determining that the amount of deposition of particulate matter trapped in the filter is abnormal when the amount of deposition of particulate matter, estimated by the deposition amount estimating means, is larger than or equal to a preset excessive deposition determination value; abnormality processing means for announcing an alarm and stopping injection of fuel from adding injectors when the excessive deposition determination means determines the amount of deposition is abnormal; vaporization determination means for determining whether moisture absorbed in the filter has vaporized; prohibiting means for prohibiting the deposition amount estimating means from estimating the amount of deposition of particulate matter when the vaporization determination means determines that moisture absorbed in the filter has not vaporized yet; and emission amount accumulation means for calculating an amount of emission of particulate matter from the internal combustion engine and calculating an accumulated amount of emission by accumulating the calculated amount of emission, wherein when the prohibiting means prohibits the deposition amount estimating means from estimating the amount of deposition of particulate matter, the excessive deposition determination means determines whether the amount of deposition of particulate matter trapped in the filter is abnormal on the basis of the accumulated amount of emission, calculated by the emission amount accumulation means.