Abstract: An excellent anti-reflection circular polarizer for preventing the reflection of external light is provided, and thereby an excellent image display device with very little degradation of anti-reflection functionality caused by decreased levels of polarization under conditions of high humidity while having little deformation of an image display panel is provided. In particular, an anti-reflection circular polarizer suitable for an organic EL image display device is provided. The anti-reflection circular polarizer includes a reflection reduction layer, a light-transmissive substrate film, a polarizing element, and a ?/4 phase-difference layer, stacked in this order, wherein the light-transmissive substrate film has a moisture permeability of 100 g/m2·day or less.