An infrared detector comprises: a reflection portion transmitting far- and middle-infrared rays and reflecting near-infrared and visible rays; a photo-current generating portion having a quantum well structure in which electrons are excited by the far- and middle-infrared rays having passed through the reflection portion so as to generate photo-current; a light emitting portion having a quantum well structure into which electrons of the photo-current generated by the photo-current generating portion are injected and the electrons thus injected thereinto are recombined with holes, thus emitting near-infrared and visible rays; and a photo-detecting portion detecting the near-infrared and visible rays emitted from the light emitting portion, and detecting the near-infrared and visible rays emitted from the light emitting portion and reflected by the reflection portion. The reflection portion, the photo-current generating portion, and the light emitting portion are made of group III-V compound semiconductors layered on a semiconductor substrate.