A condensed water treatment device for an internal combustion engine, the condensed water treatment device being applied to the internal combustion engine comprising: a selective-reduction type NOx catalyst which is provided on an exhaust passage and reduces NOx to purify exhaust gas by ammonia; an additive supplying valve which supplies additive which is ammonia or a precursor of ammonia to the exhaust passage at an upstream side of the NOx catalyst; and an EGR device which takes out the exhaust gas from the exhaust passage at a downstream side of the NOx catalyst and leads the exhaust gas taken to an intake system as EGR gas, wherein the condensed water treatment device comprises: a condensed water tank which stores condensed water generated in the EGR device; a condensed water supplying mechanism which supplies the condensed water stored in the condensed water tank to the internal combustion engine or a related device relating to the internal combustion engine; and an additive supply controlling device which is configured to increase, in a case where pH of the condensed water stored in the condensed water tank is smaller than a threshold value, a supply quantity of the additive supplied to the exhaust passage so that the supply quantity is larger than the supply quantity of a case where the pH of the condensed water stored in the condensed water tank is equal to or more than the threshold value; wherein: the additive supply controlling device is further configured to execute decrease offset of supply quantity of the additive in a decreasing quantity period following after acceleration of the internal combustion engine ends. a selective-reduction type NOx catalyst which is provided on an exhaust passage and reduces NOx to purify exhaust gas by ammonia; an additive supplying valve which supplies additive which is ammonia or a precursor of ammonia to the exhaust passage at an upstream side of the NOx catalyst; and an EGR device which takes out the exhaust gas from the exhaust passage at a downstream side of the NOx catalyst and leads the exhaust gas taken to an intake system as EGR gas, wherein the condensed water treatment device comprises: a condensed water tank which stores condensed water generated in the EGR device; a condensed water supplying mechanism which supplies the condensed water stored in the condensed water tank to the internal combustion engine or a related device relating to the internal combustion engine; and an additive supply controlling device which is configured to increase, in a case where pH of the condensed water stored in the condensed water tank is smaller than a threshold value, a supply quantity of the additive supplied to the exhaust passage so that the supply quantity is larger than the supply quantity of a case where the pH of the condensed water stored in the condensed water tank is equal to or more than the threshold value; wherein: the additive supply controlling device is further configured to execute decrease offset of supply quantity of the additive in a decreasing quantity period following after acceleration of the internal combustion engine ends. a condensed water tank which stores condensed water generated in the EGR device; a condensed water supplying mechanism which supplies the condensed water stored in the condensed water tank to the internal combustion engine or a related device relating to the internal combustion engine; and an additive supply controlling device which is configured to increase, in a case where pH of the condensed water stored in the condensed water tank is smaller than a threshold value, a supply quantity of the additive supplied to the exhaust passage so that the supply quantity is larger than the supply quantity of a case where the pH of the condensed water stored in the condensed water tank is equal to or more than the threshold value; wherein: the additive supply controlling device is further configured to execute decrease offset of supply quantity of the additive in a decreasing quantity period following after acceleration of the internal combustion engine ends. the additive supply controlling device is further configured to execute decrease offset of supply quantity of the additive in a decreasing quantity period following after acceleration of the internal combustion engine ends.