To provide a failure diagnosis method and a failure diagnosis device for a load driving circuit which can detect the abnormality of a switching time without using a jig in an inspection process at the time of manufacture and can also detect quickly the abnormality of a switching time which is found after shipping.

A DC motor M is connected to the output terminals of a motor driving circuit 1 composed of switching devices Q1-Q4 to constitute a failure diagnosis circuit for a failure diagnosis method. The switching devices Q1-Q4 are properly turned on and off and, on the other hand, the potential of the one side terminal M1 of the DC motor M is picked up from an A/D port and then given measurement conditions and a switching time measured in accordance with the conditions are applied to a predetermined algorithm to decide the failure position of the motor driving circuit 1.