To prevent a flow meter from being affected by temperature vibration of fluid and being damaged by fluid component in a device measuring fluid flow rate.

A fluid passes through the main part 2 of the flow meter. In the main part 2, the pressure on both sides of a regulator 2a works on both sides of the diaphragm 11 of a diaphragm vessel 3 and the movement of the diaphragm works of a measurement part 17 in turn. In the measurement part 17, a strain gauge 27 linked to a measurement bridge 5 is provided and the signal emitted from it can be used to show the flow rate of an orifice plate (regulator), an indication of an indication meter 7 or a record of flow rate variation or to control the flow rate to the desired value by a control system.