A strain detector is interposed between a base and an attachment member in a structure body having the base, the attachment member, and the stainless bolts fixed the base to the attachment member. The strain detector includes an elastic member and a heat flux sensor. The elastic member is provided to compress or extend in accordance with a deformation of the stainless bolts, and the elastic member generates heat based on the compression and absorbs heat based on the extension. The heat flux sensor is deformed in accordance with the compression or the extension of the elastic member and the heat in the elastic member is transferred to the heat flux sensor. The heat flux sensor can detect a magnitude of the heat flux Fh1 as a heat stream between the inside of the elastic member and the outside, generated by the compression or the extension of the elastic member.