A reducing agent injection device is equipped with a storage tank that houses a reducing agent, a pump that pressure-feeds the reducing agent, a reducing agent injection valve that injects the reducing agent pressure-fed by the pump into the inside of an exhaust pipe of an internal combustion engine, a supply path that interconnects the pump and the reducing agent injection valve, and a pressure sensor that is disposed in the supply path. The reducing agent injection device is configured such that it can suck, into the inside of the supply path, a gas inside the exhaust pipe via an injection hole in the reducing agent injection valve by subjecting the inside of the supply path to depressurization processing. An abnormality detection device detects clogging of the reducing agent injection valve in the reducing agent injection device and includes a clogging determination component. The clogging determination component uses a pressure value detected by the pressure sensor after the start of the depressurization processing to determine whether or not clogging is occurring in the reducing agent injection valve.