To provide a failure diagnosis device of a display circuit in which the type of failure can be identified for various types of failure.

A failure diagnosis device comprises an application voltage detection unit 11 which detects the actual application voltage of a display element 22, a threshold information holding unit 40 which holds the upper limit and lower limit thresholds of normal voltage range for both lighting and unlighting states of the display element, and holds the upper limit and lower limit thresholds of each range of a plurality of failure modes, and a diagnosis control unit 10 which identifies normality or abnormality on the basis of the drive state of a driver determining the lighting/unlighting of the display element, a voltage value detected, and the threshold of the threshold information holding unit, and when determined abnormal, identifies the type of failure mode on the basis of the drive state of a driver, the voltage value detected, and the threshold of the threshold information holding unit.