The disclosure relates to a method of introducing mRNA encoding Cas9 protein (Cas9 mRNA) into a mammalian embryo, comprising the steps of(a) placing a mixture of the mammalian embryo and a solution comprising Cas9 mRNA in the gap between a pair of electrodes, and(b) applying a voltage to the electrodes for a voltage application duration, wherein the voltage and the voltage application duration achieve the efficiency of mRNA introduction (R) higher than the minimum required efficiency of mRNA introduction (Rmin) that is calculated on the basis of the concentration of Cas9 mRNA (ng/μl).
