LEAK DIAGNOSIS DEVICE FOR EVAPORATED FUEL PROCESSING SYSTEM

It is a task of the invention to provide a leak diagnosis device for an evaporated fuel processing system, which is able to carry out a leak diagnosis irrespective of a temperature inside a fuel tank. A leak diagnosis device that is used in an evaporated fuel processing system including a canister (41) and a purge line (43). The canister (41) is provided inside a fuel tank (31), and adsorbs evaporated fuel that is produced inside the fuel tank (31). The purge line (43) introduces purge gas, including evaporated fuel, from the canister (41) into an intake pipe (23) of an engine (2). An alarm lamp (51) indicating an abnormality is lit on the condition that the width of decrease in the concentration of HC in the purge line (43) in a predetermined period is smaller than a predetermined threshold.