A pH sensitive carrier which is capable of developing a membrane disruptive function promoting effect, the pH sensitive carrier comprising: at least one pH sensitive compound selected from the group consisting of deoxycholic acid, cholic acid, ursodeoxycholic acid, chenodeoxycholic acid, hyodeoxycholic acid, trihydroxycholestanoic acid (C27 bile acid), glycodeoxycholic acid, glycyrrhizic acid, glycyrrhetinic acid and salts thereof; and at least one amphipathic substance selected from the group consisting of: • a phosphatidylcholine having 10 to 12 carbon atoms in the acyl group, chosen from didecanoylphosphatidylcholine and dilauroylphosphatidylcholine, • a polyoxyethylene sorbitan monofatty acid ester having 12 to 18 carbon atoms wherein said number of carbon atoms means the number of carbon atoms of a fatty acid moiety, • a sorbitan fatty acid ester having 16 to 18 carbon atoms in the acyl group, chosen from sorbitan monopalmitic acid ester (sorbitan monopalmitate), sorbitan monostearic acid ester (sorbitan monostearate), sorbitan monooleic acid ester (sorbitan monooleate), sorbitan tripalmitic acid ester (sorbitan tripalmitate), sorbitan tristearic acid ester (sorbitan tristearate) and sorbitan trioleic acid ester (sorbitan trioleate), • glycerol monooleate, • glycerol dilaurate, • glycerol distearate, • glycerol dioleate, • polyoxyethylene castor oil and • α-tocopherol wherein the pH sensitive compound is present in an amount of not less than 10 moles per 100 moles of the amphipathic substance. at least one pH sensitive compound selected from the group consisting of deoxycholic acid, cholic acid, ursodeoxycholic acid, chenodeoxycholic acid, hyodeoxycholic acid, trihydroxycholestanoic acid (C27 bile acid), glycodeoxycholic acid, glycyrrhizic acid, glycyrrhetinic acid and salts thereof; and at least one amphipathic substance selected from the group consisting of: • a phosphatidylcholine having 10 to 12 carbon atoms in the acyl group, chosen from didecanoylphosphatidylcholine and dilauroylphosphatidylcholine, • a polyoxyethylene sorbitan monofatty acid ester having 12 to 18 carbon atoms wherein said number of carbon atoms means the number of carbon atoms of a fatty acid moiety, • a sorbitan fatty acid ester having 16 to 18 carbon atoms in the acyl group, chosen from sorbitan monopalmitic acid ester (sorbitan monopalmitate), sorbitan monostearic acid ester (sorbitan monostearate), sorbitan monooleic acid ester (sorbitan monooleate), sorbitan tripalmitic acid ester (sorbitan tripalmitate), sorbitan tristearic acid ester (sorbitan tristearate) and sorbitan trioleic acid ester (sorbitan trioleate), • glycerol monooleate, • glycerol dilaurate, • glycerol distearate, • glycerol dioleate, • polyoxyethylene castor oil and • α-tocopherol • a phosphatidylcholine having 10 to 12 carbon atoms in the acyl group, chosen from didecanoylphosphatidylcholine and dilauroylphosphatidylcholine, • a polyoxyethylene sorbitan monofatty acid ester having 12 to 18 carbon atoms wherein said number of carbon atoms means the number of carbon atoms of a fatty acid moiety, • a sorbitan fatty acid ester having 16 to 18 carbon atoms in the acyl group, chosen from sorbitan monopalmitic acid ester (sorbitan monopalmitate), sorbitan monostearic acid ester (sorbitan monostearate), sorbitan monooleic acid ester (sorbitan monooleate), sorbitan tripalmitic acid ester (sorbitan tripalmitate), sorbitan tristearic acid ester (sorbitan tristearate) and sorbitan trioleic acid ester (sorbitan trioleate), • glycerol monooleate, • glycerol dilaurate, • glycerol distearate, • glycerol dioleate, • polyoxyethylene castor oil and • α-tocopherol wherein the pH sensitive compound is present in an amount of not less than 10 moles per 100 moles of the amphipathic substance.