The present invention relates to an azo compound represented by formula (1) and a salt thereof. (In the formula: A represents a naphthyl group including a substituent; R1 to R6 each independently represent a hydrogen atom, a C1-5 alkyl group, a C1-5 alkoxy group, a sulfo group, or a C1-5 alkoxy group including a sulfo group; and X represents a benzoylamino group including a substituent, a phenylamino group including a substituent, a phenylazo group including a substituent, or a naphthotriazole group including a substituent.) By using this azo compound or a salt thereof, it is possible to provide neutral-color polarizing plates, as well as color polarizing plates for liquid crystal projectors, that have excellent polarization performance and durability and that cause little color leakage in the visible-light region.