To correctly perform discrimination, even if a new instrument is added.

A time series data storage means 9 stores fluid flow rate, passing a passage 7 measured with an ultrasonic flowmeter 8, and an instrument discrimination means 12 discriminates by which instrument the change in the flow rate value stored to the time series data storing means 9 exists, on the basis of stored contents, while referring to the characteristics of a use pattern in each instrument stored to a database storing means 10. In addition, a flow rate measuring device 2 is connected through a service center 18 and a communication line 17. When the content of a database is updated by the service center 18, correct discrimination can be performed at all times, even when the new instrument is added, since the storage content of the database storing means 10 can be updated via a communication means 16.