Provided is a plasmon resonance detector that can detect temperature change in optical devices, in which the metal structure having plasmon resonance absorption is used for the optical devices. A diode formed of a conductive substrate, an n-type semiconductor layer, an i-type semiconductor layer, a p-type semiconductor layer, an n electrode (negative electrode), a p electrode (positive electrode), an insulating film, or the like is used as a semiconductor device whose resistance value changes in accordance with temperature change. A nanochain formed by connecting a plurality of metal nanoparticles is disposed on this diode. When the nanochain is irradiated with light, the nanochain generates heat. The heat generated in the nanochain is conducted to the diode. The resistance value of the diode changes in accordance with temperature change, and thus this change is read, a temperature or an amount of heat generation of the nanochain is measured, and existence and strength of the plasmon resonance are detected.