Examples of a metal complex azopyrazolone dye include dyes represented by the structural formula (I): wherein R1, R2, R3 and R4 are each independently a hydrogen atom, a halogen atom such as fluorine, chlorine and bromine, a nitro group, a linear or branched alkyl group having 1 to 5 carbon atoms, a CF3 group or an SO3(M1) group, where M1 is an alkali metal or NH4; R5 and R6 are each independently