There is provided a polarizer that can realize multi-functionalization and high-functionalization of an electronic device, such as an image display apparatus. A polarizer according to an embodiment of the present invention includes a resin film containing iodine, wherein the polarizer has formed therein a transparent portion having a transmittance higher than that of another portion, and when the polarizer is placed under an environment having a temperature of 60° C. and a humidity of 90% for 2 hours, a transmittance change (ΔTs) of the transparent portion is 10% or less.