An azo compound represented by the following formula, a tautomer thereof, or a salt of the azo compound or the tautomer: wherein, R 1 represents a (C1-C4) alkyl group; a (C1-C4) alkyl group substituted with a carboxy group; a phenyl group; a phenyl group substituted with a sulfo group; or a carboxy group, R 2 represents a cyano group; a carbamoyl group; or a carboxy group, R 3 and R 4 each independently represent a hydrogen atom; a (C1-C4) alkyl group; a halogen atom; a (C1-C4) alkoxy group; or a sulfo group, R 5 represents a (C1-C4) alkylthio group; or a (C1-C4) alkylthio group substituted with at least one kind of group selected from the group consisting of a hydroxy group, a sulfo group, and a carboxy group, R 6 represents a (C1-C4) alkylcarbonylamino group, R 7 represents a (C1-C4) alkylthio group; or a (C1-C4) alkylthio group substituted with at least one kind of group selected from the group consisting of a hydroxy group, a sulfo group, and a carboxy group, R 8 represents a (C1-C4) alkylcarbonylamino group, R 9 and R 10 each independently represent a hydrogen atom; a carboxy group; a sulfo group; an acetylamino group; a chlorine atom; a (C1-C4) alkyl group; a (C1-C4) alkoxy group; or a (C1-C4) alkoxy group substituted with at least one kind of group selected from the group consisting of a hydroxy group, a (C1-C4) alkoxy group, a sulfo group, and a carboxy group, and R 11 to R 13 each independently represent a hydrogen atom; a carboxy group; a sulfo group; a hydroxy group; an acetylamino group; a chlorine atom; a cyano group; a nitro group; a sulfamoyl group; a (C1-C4) alkyl group; a (C1-C4) alkoxy group; a (C1-C4) alkoxy group substituted with at least one kind of group selected from the group consisting of a hydroxy group, a (C1-C4) alkoxy group, a sulfo group and a carboxy group; a (C1-C4) alkylsulfonyl group; or a (C1-C4) alkylsulfonyl group substituted with at least one kind of group selected from the group consisting of a hydroxy group, a sulfo group, and a carboxy group. R 1 represents a (C1-C4) alkyl group; a (C1-C4) alkyl group substituted with a carboxy group; a phenyl group; a phenyl group substituted with a sulfo group; or a carboxy group, R 2 represents a cyano group; a carbamoyl group; or a carboxy group, R 3 and R 4 each independently represent a hydrogen atom; a (C1-C4) alkyl group; a halogen atom; a (C1-C4) alkoxy group; or a sulfo group, R 5 represents a (C1-C4) alkylthio group; or a (C1-C4) alkylthio group substituted with at least one kind of group selected from the group consisting of a hydroxy group, a sulfo group, and a carboxy group, R 6 represents a (C1-C4) alkylcarbonylamino group, R 7 represents a (C1-C4) alkylthio group; or a (C1-C4) alkylthio group substituted with at least one kind of group selected from the group consisting of a hydroxy group, a sulfo group, and a carboxy group, R 8 represents a (C1-C4) alkylcarbonylamino group, R 9 and R 10 each independently represent a hydrogen atom; a carboxy group; a sulfo group; an acetylamino group; a chlorine atom; a (C1-C4) alkyl group; a (C1-C4) alkoxy group; or a (C1-C4) alkoxy group substituted with at least one kind of group selected from the group consisting of a hydroxy group, a (C1-C4) alkoxy group, a sulfo group, and a carboxy group, and R 11 to R 13 each independently represent a hydrogen atom; a carboxy group; a sulfo group; a hydroxy group; an acetylamino group; a chlorine atom; a cyano group; a nitro group; a sulfamoyl group; a (C1-C4) alkyl group; a (C1-C4) alkoxy group; a (C1-C4) alkoxy group substituted with at least one kind of group selected from the group consisting of a hydroxy group, a (C1-C4) alkoxy group, a sulfo group and a carboxy group; a (C1-C4) alkylsulfonyl group; or a (C1-C4) alkylsulfonyl group substituted with at least one kind of group selected from the group consisting of a hydroxy group, a sulfo group, and a carboxy group.