To provide: a carboxamide derivative having reduced content of amide ester; a method for producing thereof; and a detergent composition containing the carboxamide derivative and having excellent low-temperature stability. One method for producing a carboxamide derivative is to react carboxamide, produced with a manufacturing method of carboxamide including 0.02% by weight to 0.18% by weight of amide ester, with hydrogen peroxide, wherein the method includes a carboxamide synthesis process to synthesize carboxamide by reacting diamine with fatty acid ester at a molar rate of 1.20 to 1.60. Another method for producing a carboxamide derivative is to react the carboxamide with monohaloalkylcarboxylic acid or a salt thereof. A carboxamide derivative is produced by the method for producing a carboxamide derivative. A detergent composition includes the carboxamide derivative. The carboxamide derivative is preferably amidoamine oxide or amide betaine.