A fault diagnosis device and a fault diagnosis method read a diagnostic trouble code from an Electronic Control Unit to the fault diagnosis device, and display a work guide screen for guiding work in accordance with the read diagnostic trouble code. The work guide screen includes an entire work flowchart consisting of a plurality of work items for identifying a fault occurrence location at which the fault event corresponding to the diagnostic trouble code is caused, and includes an entire work display area in which a work item selected among the plurality of work items is highlighted and a concrete work display area in which concrete work details about the highlighted work item are indicated.