SHUT-OFF VALVE FAULT DIAGNOSIS DEVICE AND FUEL SUPPLY SYSTEM

Provided is a shut-off valve fault diagnosis device that performs fault diagnosis of a first shut-off valve (41) that is disposed immediately after a gaseous fuel tank and a second shut-off valve (42) that is disposed immediately before a regulator (43) in a gaseous fuel supply system (3). The shut-off valve fault diagnosis device includes a diagnosis processing unit (67) that performs a valve-shutting control of the first shut-off valve (41), performs a valve-shutting control of the second shut-off valve (42) after a predetermined time has passed since the valve-shutting control of the first shut-off valve (41), and performs fault diagnosis of the first shut-off valve (41) and the second shut-off valve (42) based on a variation tendency in a fuel pressure between the first shut-off valve (41) and the second shut-off valve (42) after performing the valve-shutting control of the second shut-off valve (42).