A reducing agent injection valve abnormality detection device for detecting clogging of a reducing agent injection valve in a reducing agent injection device has a pressure detection component that detects the pressure inside a supply path based on a sensor value of a pressure sensor, a pump control component that fixes the output of a pump in a state where the pressure inside the supply path has become a value in a predetermined range, a reducing agent injection valve control component that opens the valve for a predetermined amount of time in a state where the output of the pump has been fixed, and a clogging determination component that determines the extent of clogging of the reducing agent injection valve by comparing, with plural threshold values, the pressure, or a pressure drop quantity, inside the supply path when the valve has been opened for the predetermined amount of time.