According to one aspect of the present invention, a method for diagnosing a failure of a flowmeter in a measuring machine, includes calculating a filling amount at an end of filling of the hydrogen gas into a tank from the measuring machine by using a pressure, a temperature, and a volume of the tank; and determining whether or not the flowmeter fails by using a plurality of error values between a metering filling amount at the end of filling measured using the flowmeter and a calculated filling amount at the end of filling calculated using the pressure, the temperature, and the volume of the tank, the plurality of error values being based on a plurality of past performance data stored in a storage device, and an error value at the end of filling of the hydrogen gas at a present time, and outputting a result.