A developer composition having improved stability to aerial oxidation, which contains at least one compound represented by formulae (A) and (B): ##STR1## where R.sub.1 and R.sub.2 each represent a hydroxyl group, an amino group, an acylamino group, an alkylsulfonylamino group, an arylsulfonylamino group, an alkoxycarbonylamino group, a mercapto group or an alkylthio group; and X represents a group of atoms selected from carbon and nitrogen which forms a 5-membered or 6-membered ring together with the two vinyl carbons substituted by R.sub.1 and R.sub.2, respectively, and the carbonyl carbon of formula (A); ##STR2## where R.sub.3 and R.sub.4 each represent a hydroxyl group, an amino group, an acylamino group, an alkylsulfonylamino group, an arylsulfonylamino group, an alkoxycarbonylamino group, a mercapto group or an alkylthio group; and Y represents a group of atoms selected from carbon, nitrogen and oxygen containing at least one ether bond, and Y forms a 6-membered ring together with the two vinyl carbons substituted by R.sub.3 and R.sub.4, respectively, and the carbonyl carbon of formula (B), provided that both R.sub.3 and R.sub.4 are not hydroxyl.