In order to transport protein encapsulated by endocytosis to cytoplasm with high efficiency, provided is a peptide represented by formula (I): R1-IWLTALKFX1GKHX2AKHX3AKQX4L-R2.(I) (In the formula, X1 is L, E or D. X2 is A, E or D. X3 is L, E, or D. X4 is Q, E, or D. At least one of X1 through X4 is E or D. R1 is a hydrogen atom, acyl group, alkoxycarbonyl group, aralkyloxycarbonyl group or aryloxycarbonyl group. R2 is a hydroxyl group (OH), amino group (NH2), S-R2a, SK-R2a, or SKL-R2a (where R2a is OH or NH2), alkoxy group, aralkyloxy group, or aryloxy group. The amino acid may be either the l-form or the d-form of an amino acid.)
