To effectively reduce the heat capacity of an infrared ray absorbing diaphragm layer and to improve the sensitivity of an element by forming a mesh structure on a part or over the entire infrared ray absorbing diaphragm layer.

A bolometer sensor type thermal infrared ray detecting element is constituted with an infrared ray reflecting film 5 on a silicon substrate 4 and a diaphragm 9 constituted of an infrared ray absorbing film 1, a diaphragm structural body 2 and a bolometer layer 3 having a prescribed mesh structure at the prescribed distance, for example. For detecting infrared images, the infrared image is made to form on the diaphragm 9, and the temperature change caused by it is detected as the resistance change of the bolometer layer 3. By making the bolometer layer 3 of a mesh structure, its heat capacity is decreased, and the sensitivity of the element is increased. The mesh structure can be also employed for the diaphragm structural body 2 and the infrared ray absorbing film 1, as long as their functions are not impaired.