A hair deforming treatment agent comprising the following components (A), (B) and (C): (A) glyoxylic acid, or a hydrate or a salt thereof, (B) a compound represented by the following formula (1): wherein R 1 represents H or a methyl group, A 1 , A 2 and B each represent H, an alkyl group, an alkenyl group, etc., D represents H, OH, a methyl group, an alkoxy group, etc., and E represents H, a methyl group, an alkoxy group, etc., and (C) water.本發明之毛髮變形處理劑含有以下之成分(A)、(B)及(C)。(A)乙醛酸或其水合物或鹽(B)式(1)所表示之化合物[R1表示H或甲基，A1、A2及B表示H、烷基、烯基等，D表示H、OH、甲基、烷氧基等，E表示H、甲基、烷氧基等](C)水
