A urea water consumption diagnostic device for urea SCR configured to suck urea water from a urea water tank with a supply pump and spray the urea water from a dosing valve disposed upstream of an SCR device via a pressurized urea water feed line, comprising: a urea water sensor configured to detect a level of the urea water in the urea water tank; spray volume instruction means configured to instruct a volume of urea water to be sprayed from the dosing valve in accordance with NOx in an exhaust gas; instructed spray volume addition means configured to add up an instructed spray volume instructed by the spray volume instruction means; consumption volume calculation means configured to calculate a cumulative consumption volume from a detection value entered from the urea water sensor; and abnormality diagnostic means configured to compare a cumulative instructed spray volume from the instructed spray volume addition means to the cumulative consumption volume from the consumption volume calculation means, and determine whether urea water spraying from the dosing valve is normal or abnormal, wherein the abnormality diagnostic means is configured to compare the cumulative instructed spray volume to the cumulative consumption volume at the time when the cumulative instructed spray volume exceeds a determination volume, configured to determine that a urea water consumption volume is abnormal when a difference between the cumulative instructed spray volume and the cumulative consumption volume exceeds a predetermined volume, and configured to determine that the urea water consumption volume is normal when the difference between the cumulative instructed spray volume and the cumulative consumption volume does not exceed the predetermined volume, wherein the consumption volume calculation means is configured to calculate a supplemented volume from a change in the level detected by the urea water sensor when supplemental urea water is supplemented to the urea water tank, sum the supplemented volume and the cumulative consumption volume, and send a sum of the supplemented volume and the cumulative consumption value to the abnormality diagnostic means, as the cumulative consumption volume, and the consumption volume calculation means is configured to repeat the reading of the level detected by the urea water sensor when an ignition key is turned on and a vehicle is in a halt condition, and update and store the level at every time when the level detected by the urea water sensor changes by the supplemental urea water being supplemented to the urea water tank. a urea water sensor configured to detect a level of the urea water in the urea water tank; spray volume instruction means configured to instruct a volume of urea water to be sprayed from the dosing valve in accordance with NOx in an exhaust gas; instructed spray volume addition means configured to add up an instructed spray volume instructed by the spray volume instruction means; consumption volume calculation means configured to calculate a cumulative consumption volume from a detection value entered from the urea water sensor; and abnormality diagnostic means configured to compare a cumulative instructed spray volume from the instructed spray volume addition means to the cumulative consumption volume from the consumption volume calculation means, and determine whether urea water spraying from the dosing valve is normal or abnormal, wherein the abnormality diagnostic means is configured to compare the cumulative instructed spray volume to the cumulative consumption volume at the time when the cumulative instructed spray volume exceeds a determination volume, configured to determine that a urea water consumption volume is abnormal when a difference between the cumulative instructed spray volume and the cumulative consumption volume exceeds a predetermined volume, and configured to determine that the urea water consumption volume is normal when the difference between the cumulative instructed spray volume and the cumulative consumption volume does not exceed the predetermined volume, wherein the consumption volume calculation means is configured to calculate a supplemented volume from a change in the level detected by the urea water sensor when supplemental urea water is supplemented to the urea water tank, sum the supplemented volume and the cumulative consumption volume, and send a sum of the supplemented volume and the cumulative consumption value to the abnormality diagnostic means, as the cumulative consumption volume, and the consumption volume calculation means is configured to repeat the reading of the level detected by the urea water sensor when an ignition key is turned on and a vehicle is in a halt condition, and update and store the level at every time when the level detected by the urea water sensor changes by the supplemental urea water being supplemented to the urea water tank.