A thermosensitive flow rate detecting element having a flat substrate is provided with a gap having an opening on at least one side thereof for the flow of a fluid, an insulating support film provided on the one side of the substrate, a sensor unit which has a heating element for heating the fluid and a thermosensitive element for detecting temperature of the fluid provided in the upper position of the opening on the insulating support film, and a fluid temperature measuring element, provided at a distance from the sensor unit on the one side of the flat substrate, for detecting temperature of the fluid. The thermosensitive flow rate detecting element measures flow rate or flow velocity of the fluid on the basis of a temperature detected by the thermosensitive element, by keeping heating temperature of the heating element at a level higher than a temperature detected by the fluid temperature measuring element by a prescribed difference in temperature. A first notch is provided on the flat substrate near the fluid temperature measuring element and is formed by removing a part of the flat substrate from either side thereof so as not to reach the remaining side thereof.