With the aim of providing a liposome, having a hydrophilic polymer introduced into the outer surface of the liposome membrane, which is a liposome capable of allowing the liposome-entrapped substance to escape from the endosome and be released into the cytoplasm, a liposome membrane component bound to the peptide shown by (a) or (b) below and a liposome membrane component bound to one end of a hydrophilic polymer the other end of which is bound to the peptide shown by (a) or (b) below are included in the liposome: (a) a peptide comprising the amino acid sequence of SEQ ID NO:1; (b) a peptide comprising the amino acid sequence of SEQ ID NO:1 with 1 or more amino acids deleted, replaced or added therein, and capable of fusing lipid membranes with one another under acidic conditions.