PROBLEM TO BE SOLVED: To provide a hairdressing agent which can increase a formation efficiency thereof when forming the hair into a nonlinear form such as curled hair.SOLUTION: The hairdressing agent which is used by applying to the hair before heating the hair to form a nonlinear form contains a modified peptide comprising one or more kinds of a structure represented by the following formula (Ia)-(Ic), and a side group having a unit selected from the salt of such structures. -S-S-(CH)-COOH (Ia) (in the formula (Ia), n is 1 or 2.) -S-S-CH(CH)-COOH (Ib) -S-S-CH(COOH)-CH-COOH (Ic)
