The present invention provides a cationic lipid, which allow nucleic acids to be easily introduced into cells, represented by formula (I)(wherein:R1 and R2 are, the same or different, each (Z)-pentadecenyl, (Z)-hexadecenyl or (Z)-heptadecenyl, etc,a and b are, the same or different, each 0 to 3,m is 1,the dotted line is a single bond or absent,X1 and X2 are hydrogen atoms, or are combined together to form a single bond or alkylene,X4 is absent or is alkylene, etcX3 is absent or is alkyl, etc,Y is absent or anion,L3 is a single bond, -CO-O- or -O-CO-R3 is hydrogen atoms, alkyl, etc,L1 and L2 are -0-, -CO-O- or -O-CO-) and the like.
