The present invention utilizes self-heating of electronic components to improve a humidity sensing part with low environment resistance, such as a condensation problem and the like, and also to enhance the heat radiation efficiency of electronic components. The humidity sensing part is used in an intake tube of an automobile by integrating, for example, with a heating resister type mass air flow measurement device. A humidity sensing element is mounted on an electronic circuit board in a mass air flow measurement device with the temperature thereof starting to increase immediately after a sensor has been actuated. This urges the temperature of the humidity sensing element to start increasing (being heated) immediately after the sensor has been actuated. To urge the humidity sensing element to be further heated, a base plate is composed of two types of materials, resin and metal. A part of the base plate holding an area of the electronic circuit board generating a large quantity of heat is composed of the metal. A part of the base plate corresponding to the periphery of the humidity sensing part which is to be heated is composed of the resin.