Provided is a spectrum detector capable of being miniaturized and which does not require complicated optical axis alignment. The spectrum detector of the present invention comprises: a substrate; a photodetector formed on the substrate and including a semiconductor having a plurality of convex portions; and a wavelength detection circuit for detecting a wavelength of light transmitted through the plurality of convex portions, from light incident on the photodetector. According to the present invention, a small-sized spectrum detector can be provided which can easily detect a peak wavelength distribution included in light of an unknown wavelength, without the use of optical equipment such as a grating or prism, thus dispensing with the need for the optical axis alignment of a complex optical system.