Abstract: A first temperature which is a temperature of exhaust gas which has passed through an exhaust gas purification treatment device is detected during supply of urea water from a urea water supply device, and a second temperature which is a temperature of exhaust gas which has passed through a second exhaust gas purification treatment device in a state where an engine in the same operating state as when the first temperature is detected and the supply of the urea water from the urea water supply device is stopped is calculated from preset data. Further, an ammonia calorific value which is an amount of heat generated in an ammonia slip catalyst device by oxidation of ammonia is calculated based on the first temperature and the second temperature, and an ammonia slip amount from the selective reduction catalyst device is calculated based on the ammonia calorific value.

Abstract: A first temperature which is a temperature of exhaust gas which has passed through an exhaust gas purification treatment device is detected during supply of urea water from a urea water supply device, and a second temperature which is a temperature of exhaust gas which has passed through a second exhaust gas purification treatment device in a state where an engine in the same operating state as when the first temperature is detected and the supply of the urea water from the urea water supply device is stopped is calculated from preset data. Further, an ammonia calorific value which is an amount of heat generated in an ammonia slip catalyst device by oxidation of ammonia is calculated based on the first temperature and the second temperature, and an ammonia slip amount from the selective reduction catalyst device is calculated based on the ammonia calorific value.