A thermo-sensitive flow rate sensor that has a flow rate detecting device, in which a heating element constituted by thermo-sensitive resistor film, is formed on a top surface of a plate-like substrate and in which a diaphragm is formed by partially removing the plate-like substrate. This sensor further has a supporting element arranged in such a way as to have a top surface that is parallel to the direction of flow of a fluid to be measured. The flow rate detecting device is supported and fixed in a recess portion formed in the supporting element so that the top surface of the device is nearly flush with the top surface of the supporting element. Further, the thin-plate-like member is attached to the back surface of the flow rate detecting device in such a way as to close a cavity.