An object of the present invention is to provide a high-sensitivity infrared sensor. According to the present invention, a support member for supporting a sensor portion in a cavity structure is formed to be remarkably thin as compared with a conventional structure, a sectional area of the support member is considerably reduced, heat conductance can remarkably be reduced and, as a result, the infrared sensor having a remarkably high sensitivity can be obtained. Moreover, according to the present invention, since an insulating layer of a support member area is etched, and a sacrifice silicon film is embedded in the area, an aspect ratio of an insulating layer RIE for forming a support leg is remarkably reduced. A manufacturing process is facilitated, a sectional area of the support leg is further reduced as a secondary effect, and the sensitivity of the infrared sensor can further be enhanced.