In a flow meter device of the present invention, a unit measuring step is defined as a procedure for measuring ultrasonic sound wave propagation times by changing the direction in which an ultrasonic sound wave is transmitted and received between a first transducer (2) and a second transducer (3), and a time measuring means (12) measures a propagation time in a forward direction and a propagation time in a reverse direction in a unit measuring step. A time difference detecting means (16) detects a difference between the propagation time in the forward direction and the propagation time in the reverse direction which are measured by the time measuring means (12). A determiner means (17) determines whether or not there is a fluid flow based on the time difference. According to presence/absence of a fluid flow, the number of times the unit measuring step is performed is determined. Therefore, it can be determined whether or not there is a fluid flow quickly in real time. A responsiveness can be improved such that a measuring method can be switched to correspond to presence/absence of a fluid flow.