A method of transferring an exogenous gene into a eukaryotic algal cell, the method including performing electroporation using multiple square-wave pulses to the solution containing a cell of a green alga with cell-wall, and a nucleic acid molecule by the following three steps: applying a square-wave electric pulse (first electric pulse) with a high voltage for a short period of time under the condition that its total electric energy falls within a predetermined range; then applying a square-wave electric pulse (second electric pulse) with a low voltage for a long period of time two or more times; and then applying a square-wave electric pulse (third electric pulse) that is opposite in polarity to the second electric pulse, with a low voltage for a long period of time, two or more times.