The present invention is a flow rate measuring mechanism provided with: a body unit that has an internal flow path through which a target fluid to be measured is configured to flow; and a pressure sensor that is attached to the body unit and senses a pressure of the internal flow path, and configured to calculate a flow rate of the fluid on the basis of the fluid pressure sensed by the pressure sensor, wherein the body unit has a length direction and a surface parallel to the length direction, which is set as a component attachment surface, and to the component attachment surface, the pressure sensor is attached such that a pressure sensitive surface thereof is substantially vertical to the component attachment surface and substantially parallel to the length direction, and thereby, without causing a reduction in pressure measurement sensitivity, makes a width direction size dramatically smaller than before.