The compound represented in formula (Ia) is provided as a novel cationic lipid which forms lipid particles; also provided are a lipid particle containing said compound, a nucleic acid lipid particle containing said lipid particle, and a drug containing said nucleic acid lipid particle as the effective ingredient.本發明係關於一種形成脂質粒子之作為新穎陽離子性脂質之式(Ia)記載的化合物之提供、一種含該化合物的脂質粒子之提供、一種含該脂質粒子的核酸脂質粒子、一種含有該核酸脂質粒子作為有效成分的醫藥。