According to one embodiment, there is provided a method of producing a gene modification T cell (CAR-T cells) which expresses a chimeric antigen receptor (CAR). This method includes stimulating a cell population containing a T cell with an antibody which activates the T cell, bringing the cell population into contact with a nucleic acid-introducing carrier, wherein the nucleic acid-introducing carrier containing a lipid particle, a first nucleic acid and containing a CAR gene, and a second nucleic acid containing a transposase gene encapsulated in the lipid particle, and culturing the cell population after the contacting.