Flow rate measuring device and flow rate calculation method

A flow rate measuring device comprises a first oscillator (2), a second oscillator (3), a controller (100), a clock unit (10), and a computing unit (200). The computing determines whether the time difference between the transmission time in the forward direction and transmission time in the reverse direction is less than a prescribed value, calculates, when the difference is determined to be less than the prescribed value, a correction amount for the transmission time on the basis of the time difference, and calculates the flow rate of the fluid using the correction amount for the transmission time.