To provide a flow regulating instrument having high measurement accuracy and reducing the process regarding the flow rate measurement, while being miniaturized.

Flow regulating plates 14 mounted on a part of a flow passage 53 in a flow rate measuring device in which a flow sensor is installed have the same length in front and behind the flow sensor along the direction of the flow. A first mesh 15A and a second mesh 15B are disposed at the part of the flow passage 53 where the flow sensor is disposed, so as to sandwich the flow regulating plates 14. Further, a third mesh 15C and a fourth mesh 15D are provided on the upstream side of the first mesh 15A and the downstream side of the second mesh 15B at prescribed intervals, respectively. The first mesh 15A and the second mesh 15B have the equivalent structure, and are disposed symmetrically along the direction of the flow so as to sandwich the flow sensor. The third mesh 15C and the fourth mesh 15D have the equivalent structure, and are disposed symmetrically along the direction of the flow so as to sandwich the flow sensor.