Disclosed is a simple and highly efficient method for introducing a gene into a target cell using a retrovirus vector. The method comprises the steps of (a) placing a liquor containing a retrovirus vector having a foreign gene carried thereon into a bag for cell culture on which a retrovirus-binding substance has been immobilized, and incubating the liquor at a temperature lower than 25° C. for 8-48 hours, thereby producing a culture bag having the retrovirus vector bound thereto, (b) adding a target cell to the culture bag that has been produced in step (a) and incubating the culture bag for 8 hours or less, and (c) flipping the culture bag upside down and incubating the culture bag. The gene introduction method is useful particularly in medicine, cell technology, gene technology, and embryologic technology.