A decrease in determination accuracy on filter trouble due to a decrease in detection accuracy of a PM sensor is restricted. A filter, a selective reduction type NOx catalyst provided on a downstream of the filter, the PM sensor detecting an amount of PM on a downstream of the selective reduction type NOx catalyst, and a removal section conducting a process for removing a reducing agent attached to the PM sensor in a case where at least one of conditions is satisfied that a temperature of the selective reduction type NOx catalyst is equal to or lower than a threshold, that a temperature of the exhaust is equal to or lower than a threshold, that a flow rate of the exhaust is equal to or higher than a threshold, and that an adsorption amount of the reducing agent in the selective reduction type NOx catalyst is equal to or larger than a threshold are included.