An infrared light detector with an infrared light sensitivity thereof further improved. According to the infrared light detector, an isolated region of a first electronic layer is switched between a “disconnected status” and a “connected status”. Under the connected status, saturation of an electrostatic charge quantity of the isolated region in the disconnected status is eliminated, and consequently, saturation of a variation amount of an electrical conductivity of a second electronic layer is eliminated. Therefore, the infrared light sensitivity is further improved by time integration of the variation amount of the electrical conductivity of the second electronic layer.