INJECTOR FAILURE DIAGNOSTIC DEVICE AND INJECTOR FAILURE DIAGNOSTIC METHOD

An injector failure diagnostic device diagnoses injector failures for a multi-cylinder internal combustion engine having injectors to each injector injects fuel to the corresponding cylinder. The injector failure diagnostic device includes: an operating sound obtainment unit configured to obtain current operating sound that is operating sound when all of the injectors operate, and obtain pseudo-failure operating sound sequentially for each of the injectors, the pseudo-failure sound being operating sound generated by stopping the fuel injection from one injector while maintaining the operation of the remaining injectors; and a faulty injector identification unit configured to determine whether or not the pseudo-failure operating sound of each injector obtained by the operating sound obtainment unit is similar to the current operating sound to identify a faulty injector.