PROBLEM TO BE SOLVED: To obtain a new carboxylic acid compound containing a sulfonyl group having excellent cement-dispersing property, and useful as a cement additive, a cement dispersing agent, a cement water-reducing agent, a washing builder, a chelating agent or the like. SOLUTION: A compound of formula I X is (CH2)n1CHR1COOM (n1=0-2; R1 is H, OH or SO3M; M is H or an alkali metal); Y is H, (CH2)n2CHR2COOM (n2 is same as n1; R2 is same as R1) or the like; Z is formula II (n3 is same as n1), formula III, formula IV [n4 is same as n1; R5 is H or methyl; A2 is NH or O; M is H, an alkali metal, an alkaline earth metal; zinc, an amine or the like] or the like; A1 is nitrogen or oxygen}, for example, a compound of formula V. A compound of formula I can be obtained, for example, by heating an aqueous solution containing sodium sulfomaleate and disodium salt of aspartic acid at 50-150 deg.C.