An agent for hair deforming treatment comprising the following components (A) to (C): (A) glyoxylic acid or a hydrate or salt thereof, (B) a compound represented by the following formula (1): wherein R 1 represents H or a methyl group, X represents H, OH, or a methoxy group, Y represents H, O, OH, or a methoxy group, Z represents H, an alkyl group, etc., R x represents H, O, a methoxy group, etc., R y represents H, OH, an aromatic hydrocarbon group, etc., and the dashed line optionally represents a double bond, and (C) water, wherein the molar ratio of the content of the component (B) to the content of the component (A), (B)/(A), is 0.01 or more and 5 or less.
