Provided are a polarizer having a high degree of alignment and an image display device including the polarizer. The polarizer of the present invention is a polarizer which is formed of a polarizer-forming composition containing a liquid crystal compound and a dichroic material, in which the liquid crystal compound and the dichroic material are horizontally aligned, and in an X-ray diffraction spectrum of the polarizer, at least one of a plurality of peaks observed in a diffraction angle range of 17° or less is a peak A in which an interval of a periodic structure corresponding to the at least one peak does not have an integer multiple relationship with an interval of a periodic structure corresponding to at least one of other peaks.