A flow rate measuring device simplifies calculation, reduces memory required for calculation, absorbs variations due to manual operation and, depending on the state of ignition, improves the accuracy of appliance identification by extracting features of appliances. The flow rate measuring device includes: a difference value conversion unit that converts into codes difference values of the flow rate measured at constant time intervals by an ultrasonic flowmeter; an appliance feature extraction unit creates an appliance feature code string indicating a feature of each appliance by, for example, making comparison and judgment using a third last code, a second last code, a last code and a current code of the codes obtained at constant time intervals, and by performing code deletion; and an identification unit performs appliance identification by comparing the appliance feature code string with an appliance inherent feature code string indicating the feature code string inherent in each appliance.