An object is to suppress the occurrence of a failure in supply of urea water as much as possible in filling control of urea water in a pump share-type urea water supply system with two supply valves. In the pump share-type urea water supply system with a first supply valve and a second supply valve, a urea water tank is connected with the respective supply valves by a urea water supply path. The urea water supply path includes a first supply path for the first supply valve and a second supply path for the second supply valve. The second supply path has a larger capacity than the capacity of the first supply path by a predetermined volume. Filling control of urea water pressure-feeds urea water to the first supply valve and the first supply path by a pump operated in a specified operating state in a state that at least the first supply valve out of the first and second supply valves is opened, and closes the first supply valve based on a pressure value or a pressure variation per unit time obtained by an acquirer.