An abnormality diagnosis system is applied to a fuel supply system including a fuel pump that pumps fuel from a fuel tank and a fuel pipe in which fuel discharged from the fuel pump flows. The abnormality diagnosis system stores a minimum fuel pressure in the fuel pipe in one trip after a main switch of the fuel supply system is turned on and until the main switch is turned off and data indicating a state when the minimum fuel pressure was recorded as diagnosis data in a storage device. In the abnormality diagnosis system, an execution device determines a failure spot associated with a decrease in fuel pressure in the fuel pipe using the diagnosis data stored in the storage device and diagnoses an abnormality of the fuel supply system.