Provided is a polarizer durable against high-temperature and high-humidity conditions, small in changes in the single plate transmittance, and a liquid crystal display device. A polarizer including a polyvinyl alcohol-based resin, a dichroic colorant, and a compound, etc. represented by the formula (1) below, the content of the compound represented by the formula (1) being 0.01 to 30 parts by mass relative to 100 parts by mass of the polyvinyl alcohol-based resin. In the formula (1) , each of R1 and R3 independently represents a hydrogen atom, C1-20 straight-chain alkyl group, C3-20 branched alkyl group, C3-20 cycloalkyl group, C2-20 alkenyl group or C6-20 aromatic group, and R5 represents a substituent.