A flow meter device for measuring a flow rate of a fluid passing through a conduit, the flow meter device comprising: a first vibrator and a second vibrator, each of which is provided on the conduit and configured to transmit and receive an ultrasonic signal; a control unit configured to intermittently switch transmitting and receiving vibrators of the ultrasonic signal between the first vibrator and the second vibrator; a timekeeper configured to measure a propagation time of the ultrasonic signal in a forward direction from the first vibrator to the second vibrator, and measure a propagation time of the ultrasonic signal in a reverse direction from the second vibrator to the first vibrator; an arithmetic operation unit configured to calculate the flow rate of the fluid based on the propagation times of the ultrasonic signal; and a gas leakage detection function using a reference flow rate for determining the presence or absence of minute gas leakage, characterized in that the arithmetic operation unit is configured to: determine whether or not a time difference between the propagation time in the forward direction and the propagation time in the reverse direction is less than a predetermined value that is less than a propagation time difference that corresponds to the reference flow rate for determining presence or absence of minute gas leakage; calculate a propagation time correction amount based on the time difference if it is determined that the time difference is less than the predetermined value; and calculate the flow rate of the fluid by using the propagation time correction amount. a first vibrator and a second vibrator, each of which is provided on the conduit and configured to transmit and receive an ultrasonic signal; a control unit configured to intermittently switch transmitting and receiving vibrators of the ultrasonic signal between the first vibrator and the second vibrator; a timekeeper configured to measure a propagation time of the ultrasonic signal in a forward direction from the first vibrator to the second vibrator, and measure a propagation time of the ultrasonic signal in a reverse direction from the second vibrator to the first vibrator; an arithmetic operation unit configured to calculate the flow rate of the fluid based on the propagation times of the ultrasonic signal; and a gas leakage detection function using a reference flow rate for determining the presence or absence of minute gas leakage, characterized in that the arithmetic operation unit is configured to: determine whether or not a time difference between the propagation time in the forward direction and the propagation time in the reverse direction is less than a predetermined value that is less than a propagation time difference that corresponds to the reference flow rate for determining presence or absence of minute gas leakage; calculate a propagation time correction amount based on the time difference if it is determined that the time difference is less than the predetermined value; and calculate the flow rate of the fluid by using the propagation time correction amount. determine whether or not a time difference between the propagation time in the forward direction and the propagation time in the reverse direction is less than a predetermined value that is less than a propagation time difference that corresponds to the reference flow rate for determining presence or absence of minute gas leakage; calculate a propagation time correction amount based on the time difference if it is determined that the time difference is less than the predetermined value; and calculate the flow rate of the fluid by using the propagation time correction amount.