A salt represented by formula (I): In formula (I), R1, R2, R3 and R4 each independently represent a halogen atom or a perfluoroalkyl group having 1 to 6 carbon atoms, R5, R6 and R7 each independently represent a halogen atom, a hydroxy group, a fluorinated alkyl group having 1 to 6 carbon atoms or an alkyl group having 1 to 12 carbon atoms, and —CH2— included in the alkyl group may be replaced by —O— or —CO—, m5 represents an integer of 0 to 3, m6 represents an integer of 0 to 3, m7 represents an integer of 0 to 3, R8 and R9 each independently represent a hydrogen atom or an alkyl group having 1 to 12 carbon atoms, and —CH2— included in the alkyl group may be replaced by —O— or —CO—, and Al− represents an organic anion.