An object of the present invention is to provide a carboxylic acid-type lipid that can accelerate adhesion or aggregation of platelets even if the carboxylic acid-type lipid does not carry a protein involved in adhesion or aggregation of platelets, such as GPIb and H12, or a peptide corresponding to an active site of the protein; a lipid particle and a lipid membrane each comprising the carboxylic acid-type lipid; and a platelet aggregation accelerating agent, a platelet adhesion accelerating agent, a hemostatic agent and a platelet substitute each comprising the carboxylic acid-type lipid, the lipid particle or the lipid membrane, and, in order to achieve the object, the present invention provides a carboxylic acid-type lipid selected from carboxylic acid-type lipids represented by formulas (I) to (VI), a lipid particle comprising the carboxylic acid-type lipid, a lipid membrane comprising the carboxylic acid-type lipid, and a platelet aggregation accelerating agent, a platelet adhesion accelerating agent, a hemostatic agent and a platelet substitute each comprising the carboxylic acid-type lipid, the lipid particle or the lipid membrane.