An iodine-based polarizer includes a polyvinyl alcohol-based film; and iodine adsorbed and oriented in the polyvinyl alcohol-based film, the iodine-based polarizer having be undergone a treatment with a treatment bath containing at least one reducing agent, the iodine-based polarizer containing an oxidized form of the reducing agent, wherein the total content of the reducing agent and the oxidized form is from 0.06×10−6 mol/g to 1.6×10−6 mol/g. The iodine-based polarizer has a sufficiently high level of transmittance, degree of polarization, and other optical properties and can suppress light leakage in short-wavelength.