A photothermal converter using a wavelength selective perfect absorber made of a low-loss metal material or dielectric and a heat detection sensor are combined to develop a sensor that efficiently converts light of a specific wavelength into heat and further electrically detects the heat. Here, since the wavelength selective perfect absorber of the present invention has a periodic structure, it has high directivity, and can also be used as a small motion sensor or a watching sensor using detection of thermal radiation. In addition, it can also be used as a high-precision small position sensor by being combined with a laser light source matching the resonance wavelength of the sensor.